Patent Application
20060125709
This invention relates to wireless communication systems, and more particularly to an antenna apparatus for use by mobile subscriber units in a TDMA, CDMA, FDMA, or GSM wireless network or by a client station in an Wireless Local Area Network (WLAN), such as an 802.11 network, to provide beamforming transmission and reception capabilities.
Code Division Multiple Access (CDMA) communication systems may be used to provide wireless communications between a base station and one or more mobile subscriber units. The base station is typically a computer controlled set of transceivers that are interconnected to a land-based public switched telephone network (PSTN). The base station includes an antenna apparatus for sending forward link. radio frequency signals to the mobile subscriber units. The base station antenna is also responsible for receiving reverse link radio frequency signals transmitted from each mobile unit. Each mobile subscriber unit also contains an antenna apparatus for the reception of the forward link signals and for transmission of the reverse links signals. A typical mobile subscriber unit is a digital cellular telephone handset or a personal computer coupled to a cellular modem. In CDMA cellular systems, multiple mobile subscriber units may transmit and receive signals on the same frequency but with different codes, to permit detection of signals on a per unit basis.
The most common type of antenna used to transmit and receive signals at a mobile subscriber unit is a mono- or omni-pole antenna. This type of antenna consists of a single wire or antenna element that is coupled to a transceiver within the subscriber unit. The transceiver receives reverse link signals to be transmitted from circuitry within the subscriber unit and modulates the signals onto the antenna element at a specific frequency assigned to that subscriber unit. Forward link signals received by the antenna element at a specific frequency are demodulated by the transceiver and supplied to processing circuitry within the subscriber unit.
The signal transmitted from a monopole antenna is omnidirectional in nature. That is, the signal is sent with the same signal strength in all directions in a generally horizontal plane. Reception of a signal with a monopole antenna element is likewise omnidirectional. A monopole antenna does not differentiate in its ability to detect a signal in one direction versus detection of the same or a different signal coming from another direction.
A second type of antenna which may be used by mobile subscriber units is described in U.S. Pat. No. 5,617,102. The system described therein provides a directional antenna comprising two antenna elements mounted on the outer case of a laptop computer. The system includes a phase shifter attached to the two elements. The phase shifter may be switched on or off in order to affect the phase of signals transmitted or received during communications to and from the computer. By switching the phase shifter on, the antenna transmit pattern may be adapted to a predetermined hemispherical pattern which provides transmit beam pattern areas having a concentrated signal strength or gain. The dual element antenna directs the signal into predetermined quadrants or hemispheres to allow for large changes in orientation relative to the base station while minimizing signal loss.
CDMA cellular systems are also recognized as being interference limited systems. That is, as more mobile subscriber units become active in a cell and in adjacent cells, frequency interference becomes greater and thus error rates increase. As error rates increase, maximum data rates decrease. Thus, another method by which data rate can be increased in a CDMA system is to decrease the number of active mobile subscriber units, thus clearing the airwaves of potential interference. For instance, to increase a current maximum available data rate by a factor of two, the number of active mobile subscriber units can be decreased by one half. However, this is rarely an effective mechanism to increase data rates due to a lack of priority amongst users.
Various problems are inherent in prior art antennas used on mobile subscriber units in wireless communications systems, such as CDMA cellular systems, and client stations in Wireless Local Area Network (WLAN) systems, e.g., 802.11 systems. One such problem is called multipath fading. In multipath fading, a radio frequency signal transmitted from a sender (either base station or mobile subscriber unit) may encounter interference on route to an intended receiver. The signal may, for example, be reflected from objects such as buildings that are not in the direct path of transmission, but that redirect a reflected version of the original signal to the receiver. In such instances, the receiver receives two versions of the same radio signal: the original version and a reflected version. Since each received signal is at the same frequency but the reflected signal may be out of phase with the original due to reflection and a longer transmission path, the original and reflected signals may tend to cancel each other out. This results in fading or dropouts in the received signal, hence the term multipath fading.
Single element antennas are highly susceptible to multipath fading. A single element antenna has no way of determining the direction from which a transmitted signal is sent and cannot be tuned or attenuated to more accurately detect and receive a signal in any particular direction.
The dual element antenna described in the aforementioned reference is also susceptible to multipath fading, due to the symmetrical nature of the hemispherical lobes formed by the antenna pattern when the phase shifter is activated. Since the lobes created in the antenna pattern are more or less symmetrical and opposite from one another, a signal reflected in a reverse direction from its origin can be received with as much power as the original signal that is directly received. That is, if the original signal reflects from an object beyond or behind the intended receiver (with respect to the sender) and reflects back at the intended receiver from the opposite direction as the directly received signal, a phase difference in the two signals can create a multipath fading situation.
Another problem present in cellular communication systems is intercell interference. Most cellular systems are divided into individual cells, with each cell having a base station located at its center. The placement of each base station is arranged such that neighboring base stations are located at approximately sixty degree intervals from each other. In essence, each cell may be viewed as a six sided polygon with a base station at the center. The edges of each cell adjoin each other and many cells form a honeycomb like image if each cell edge were to be drawn as a line and all cells were viewed from above. The distance from the edge of a cell to its base station is typically driven by the maximum amount of power that is to be required to transmit an acceptable signal from a mobile subscriber unit located near the edge of a cell to that cell's base station (i.e., the power required to transmit an acceptable signal a distance equal to the radius of one cell).
Intercell interference occurs when a mobile subscriber unit near the edge of one cell transmits a signal that crosses over the edge of a neighboring cell and interferes with communications taking place within the neighboring cell. Typically, intercell interference occurs when similar frequencies are used for communication in neighboring cells. The problem of intercell interference is compounded by the fact that subscriber units near the edges of a cell typically use higher transmit powers so that the signals they transmit can be effectively received by the intended base station located at the cell center. Consider that another mobile subscriber unit located beyond or behind the intended receiver may be presented at the same power level, representing additional interference.
The intercell interference problem is exacerbated in CDMA systems, since the subscriber units in adjacent cells may typically be transmitting on the same frequency. What is needed is a way to reduce the subscriber unit antenna's apparent field of view, which can have a marked effect on the operation of the forward link (base to subscriber unit or access point to client station) by reducing the apparent number of interfering transmissions. A similar improvement is needed for the reverse link, so that the transmitted signal power needed to achieve a particular receive signal quality could be reduced.
Accordingly, the present invention provides an inexpensive antenna apparatus for use with a mobile subscriber unit in a wireless same frequency communication system, such as a CDMA cellular communication system, or for use with a client station in a WLAN system, such as an 802.11 system, employing same frequency techniques or multiple frequency band techniques.
The present invention provides a precise mechanism for determining in which direction the base station or access point assigned to the mobile subscriber unit or client station, respectively, is located and provides a means for configuring the antenna apparatus to maximize the effective radiated and/or received energy. The antenna apparatus includes at least one active antenna element that transmits and receives RF energy, multiple passive antenna elements that re-radiate the RF energy, and a like number of selective impedance components, each respectively coupled to one of the passive antenna elements. The selectable impedance components are independently adjustable (i.e., programmable) to affect the direction of the beam produced by the directive antenna. Thus, forward and reverse links have improved gain.
The selectable impedance components are independently adjustable to make the associated antenna elements reflective or transmissive. Reflective antenna elements are, in effect, elongated, causing reflection of RF signals. Transmissive antenna elements are, in effect, shortened, allowing RF signals from the active antenna element(s) to propagate past them. Through proper coordination of the passive antenna elements, the subscriber unit uses the directive antenna to direct the beam to reduce multipath fading and intercell interference.
In one embodiment, the antenna apparatus is allowed to adapt to various orientations with respect to the base station or access point. In this embodiment, the antenna apparatus also includes a controller coupled to the selectable impedance components. The controller determines an optimal impedance setting for each selectable impedance component. The proper phase, set by the associated impedance component, of each passive antenna element may, for example, be determined by monitoring an optimum response to a pilot signal transmitted from the base station or access point. The antenna apparatus thus acts as a beamformer for transmission of signals from the subscriber unit or client station and acts as a directive antenna for signals received by the subscriber unit or client station.
Through the use of an array having at least one active antenna element and multiple passive antenna elements each having a programmable re-radiation phase, the antenna apparatus is estimated to increase the effective transmit power per bit transmitted by as much as 3 decibels (dB) for reverse link communications over classic phased array antenna configurations, which provide 4.5 dB. Thus, the number of active subscriber units or client stations in a cell may remain the same while the antenna apparatus of this invention increases data rates for each subscriber unit or client station beyond those achievable by prior art antennas. Alternatively, if data rates are maintained at a given rate, more subscriber units or client stations may be active at the same time in a single cell using the antenna apparatus described herein. In either case, the capacity of a cell is increased, as measured by the sum total of data being communicated at any moment in time.
Forward link communication capacity can be increased as well, due to the directional reception capabilities of the antenna apparatus. Since the antenna apparatus is less susceptible to interference from adjacent cells, the forward link capacity can be increased by adding more users or by increasing cell radius size.
The base station or access point may also be equipped with a directional antenna apparatus and execute processes associated with the operation of the antenna apparatus as described in reference to operation by a subscriber unit or client station.
With respect to the physical implementation of the antenna apparatus, one embodiment of the invention specifies that a central, active, antenna element is encircled by multiple passive antenna elements mounted on a planar surface having a single ground plane layer. Electrical coupling to the ground plane is implemented through switches coupling the associated antenna elements to respective, fixed, impedance components, such as a delay line, capacitor, inductor, lumped impedance, or adjustable impedance component, such as a varactor. Other embodiments specify that more than one active antenna element is employed along with an associated feed network, forming an antenna array surrounded by multiple, passive, antenna elements.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
is a flow chart of steps performed by a perturbational algorithm to optimally determine the phase settings of antenna elements;
A description of preferred embodiments of the invention follows.
Continuing to refer to
It is also to be understood by those skilled in the art that
The invention provides the mobile subscriber units 60 with an antenna 100 that provides directional reception of forward link radio signals transmitted from base station 160, as well as providing directional transmission of reverse link signals, via a process called beamforming, from the mobile subscriber units 60 to the base station 160. This concept is illustrated in
It should be understood that the base station 160 may also be equipped with a directional antenna apparatus 100. The base station 160 generally operates in omni-directional mode but may engage the directivity properties of the antenna apparatus 100 for similar reasons as a subscriber unit 60 or reasons particular to a base station 160, such as peak time of day reasons (e.g., rush hour highway traffic), priority service, emergency service, and so forth. Thus, the description below is presented with respect to a subscriber unit 60 using the antenna apparatus 100; however, the same principles apply to the base station 160 employing the antenna apparatus 100.
In a preferred embodiment, each antenna element 101 through 105 is disposed on the surface of the housing 110 as illustrated in the figure. In this preferred embodiment, four elements 101, 102, 104 and 105 are respectively positioned at locations corresponding to corners of a square, and a fifth antenna element 103 is positioned at a location corresponding to a center of the square. The distance between each element 101 through 105 is great enough so that the phase relationship between a signal received by more than one element 101 through 105 will be somewhat out of phase with other elements that also receive the same signal, assuming all elements 101 through 105 have the same phase setting as determine by phase shifters 111 through 115. That is, if the phase setting of each element 101 through 105 were the same, each element 101 through 105 would receive the signal somewhat out of phase with the other elements.
However, according to the operation of the apparatus antenna 100 in this invention, the phase shifters 111 through 115 are independently adjustable to affect the directionality of signals to be transmitted and/or received to or from the subscriber unit (i.e., laptop computer 150 in this example). By properly adjusting the phase for each element 101 through 105, during signal transmission, a composite beam is formed which may be positionally directed towards the base station 160. That is, the optimal phase setting for sending a reverse link signal 170 from the antenna apparatus 100 is a phase setting for each antenna element 101 through 105 that creates a directional reverse link signal beamformer. The result is an antenna apparatus 100 which directs a stronger reverse link signal pattern in the direction of the intended receiver base station 160.
The phase settings used for transmission also cause the elements 101 to 105 to optimally receive forward link signals 180 that are transmitted from the base station 160. Due to the programmable nature and the independent phase setting of each element 101 through 105, only forward link signals 180 arriving from a direction that is more or less in the location of the base station 160 are optimally received. The elements 101 through 105 naturally reject other signals that are not transmitted from a similar location as are the forward link signals. In other words, a directional antenna is formed by independently adjusting the phase of each element 101 through 105.
The summation network 120 is coupled to the signal terminal 15 of each phase shifter 111 through 115. During transmission, the summation network 120 provides respective reverse link signals to be transmitted by each of the phase shifters 111 through 115. The phase shifters 111 through 115 shift the phase of the reverse link signal by a phase setting associated with that particular phase shifter 111 through 115, respectively, as set by a phase shift control input, p. By shifting the phase of the transmitted reverse link signals 170 from each element 101 through 105, certain portions of the transmitted signal 170 that propagates from each element 101 through 105 will be more in phase with other portions of other signals 170 from other elements 101 through 105. In this manner, the portions of signals that are more in phase with each other will combine to form a strong composite beam for the reverse link signals 170. The amount of phase shift provided to each antenna element 101 through 105 determines the direction in which the stronger composite beam will be transmitted.
The phase settings used for transmission from each element 101 through 105, as noted above, provide a similar physical effect on a forward link frequency signal 180 that is received from the base station 160. That is, as each element 101 through 105 receives a signal 180 from the base station 160, the respective received signals will initially be out of phase with each other due to the location of each element 101 through 105 upon base 110. However, each received signal is phase-adjusted by the phase shifters 111 through 115. The adjustment brings each signal in phase with the other received signals 180. Accordingly, when each signal is summed by the summation network 120, the composite received signal will be accurate and strong.
To optimally set the phase shift for each phase shifter 111 through 115 in antenna 100, phase control values are provided by the controller 140. Generally, in the preferred embodiment, the controller 140 determines these optimum phase settings during idle periods when laptop computer 150 is neither transmitting nor receiving data via antenna 100. During this time, a received signal, for example, a forward link pilot signal 190, that is continuously sent from base station 160 and that is received on each antenna element 101 through 105. That is, during idle periods, the phase shifters 111 through 115 are adjusted to optimize reception of the pilot signal 190 from base station 160, such as by maximizing the received signal energy or other link quality metric.
The processor 140 thus determines an optimal phase setting for each antenna element 101 through 105 based on an optimized reception of a current pilot signal 190.
The processor 140 then provides and sets the optimal phase for each adjustable phase shifter 111 through 115. When the antenna apparatus 100 enters an active mode for transmission or reception of signals between the base station 160 and the laptop 150, the phase setting of each phase shifter 111 through 115 remains as set during the previous idle time period.
Before a detailed description of phase setting computation as performed by the processor 140 is given, it should be understood that the invention is based in part on the observation that the location of the base station 160 in relation to any one mobile subscriber unit (i.e., laptop 150) is approximately circumferential in nature. That is, if a circle were drawn around a mobile subscriber unit and different locations are assumed to have a minimum of one degree of granularity between any two locations, the base station 160 can be located at any of a number of different possible angular locations.
Assuming accuracy to one degree, for example, there are 360 different possible phase setting combinations that exist for an antenna 100. Each phase setting combination can be thought of as a set of five phase shift values, one for each antenna element 101 through 105.
There are, in general, at least two different approaches to finding the optimized phase shift values. In the first approach, the controller 140 performs a type of optimized search in which all possible phase setting combinations are tried. For each phase setting (in this case, for each one of the 360 angular settings), five precalculated phase values are read, such as from memory storage locations in the controller 140, and then applied to the respective phase shifters 111 through 115. The response of the receiver 130 is then detected by the controller 140. After testing all possible angles, the one having the best recover response, such as measured by maximum signal to noise ratio (the ratio of energy per bit, Eb, or energy per chip, Ec, to total interference, Io).
In a second approach, each phase shift value is individually determined by allowing it to vary while the other phase values are held constant. This perturbational approach iteratively arrives at an optimum value for each of the five phase settings.
In step 301, the controller 140 determines that the idle mode has been entered, such as by detecting certain forward link signals 180. Step 302 then begins a loop that will execute once for each possible angle or location at which the base station 160 may be located. In the preferred embodiment, this loop is executed 360 times. Step 303 then programs each phase shifter 111 through 115 with a phase setting corresponding to the first location (i.e., angle 0) setting. The phase settings may, for example, be precalculated and stored in a table, with five phase shift setting for each possible angle corresponding to the five elements of the array. In other words, step 303 programs phase settings for a first angle, which may be conceptualized as angle 0 in a 360 degree circle surrounding the mobile subscriber unit 60. Step 304 then measures the received pilot signal 190, as output from the summation network 120. The measurement in step 304 reflects how well each antenna element 101 through 105 detected the received pilot signal 190 based upon the current set of programmed phase settings applied in step 303. Step 304 saves the measurement as a received signal metric value. The metric may, for example, be a link quality metric as bit error rate or noise energy level per chip (Ec/No).
Step 305 then returns processing to step 302 to program the phase shifters for the next set of phase settings. Steps 302 through 305 repeat until all 360 sets of phase settings have been programmed into phase shifters 111 through 115 (step 303) and a measurement has been taken of the received pilot signal 190 for each of these settings (Step 304). After step 305 determines there are no more set of phase settings, step 306 determines the best set of phase settings as determined by which settings produced the strongest receive signal metric value. Step 307 then programs the phase shifters 111 through 115 with the set of phase settings that was determined to produce this best result.
During long periods of idle time, step 308 is executed which repeats the process periodically. Step 308 accounts for the fact that the antenna 100 might be moved and re-oriented during idle periods, thus affecting the direction and orientation of the base station in relation to the antenna 100.
In addition, the antenna may be optimized during transmission. In this manner, steps 301 through 308 continuously update and set optimal phase setting for each antenna element 101 through 105.
In step 401, one of the antenna elements 101 through 105 is selected. In step 402, the phase settings of the four remaining elements not selected in step 400 are fixed in value. Step 403 then varies the phase setting of the non-fixed element selected in step 401 until the setting which maximizes the pilot signal metric is determined. Then, the process repeats by returning to step 401 where the previously selected element is fixed to this optimum phase and the phase setting of one of the other elements is varied. The process continues until each element is configured with an optimal setting. As the process iterates, the phase settings of each element converge to an optimum setting.
The process fixes a value for four of the five unknown, optimum phase shifts W[i], e.g. W[2] through W[5]. The process perturbs the system and observes the response, adapting to find the optimum value for the unfixed phase value, e.g. W[1]. The measured link quality metric, in this case Ec/Io, is fed to a first gain block G1. Again input G is fed to a second gain block G2. A first fast “clock” date value, CLK1, which alternates from a value of “1” to a value of “−1” is inverted by I1 and fed to a first multiplier M1. The other input of multiplier M1 is fed by the gain block G2.
The output of ml is fed to a second multiplier M2 together with the output of GI. An integrator N1 measures an average level and provides this to the latch L. A slow clock CLK2, typically alternating at a rate which varies between “1” and “0” and is much slower than CLK1, by at least 100 times, drives the latch “clock” C. The output of the latch L is summed by summation block S with the non-inverted output of M2. The result, W[i], is a value which tends to seek a localized minima of the function.
The process shown in
Alternatively, instead of varying a phase assigned to each antenna element 101 through 105, the phase setting for each element can be stored in a table of vectors, each vector having assignments for the five elements 101 through 105. The five values in each vector can be computed based upon the angle of arrival of the received pilot signal. That is, the values for each antenna element are set according to the direction in which the base station is located in relation to the mobile subscriber unit. The angle of arrival can be used as a value to lookup the proper vector of weights (and/or phase settings) in the table. By using a table with vectors, only the single angle of arrival calculation needs to be performed to properly set the phase settings of each element 101 through 105.
The antenna apparatus in preferred embodiments of the invention is inexpensive to construct and greatly increases the capacity in a CDMA interference limited system. That is, the number of active subscriber units within a single cell in a CDMA system is limited in part by the number of frequencies available for use and by signal interference limitations that occur as the number of frequencies in use increases. As more frequencies become active within a single cell, interference imposes maximum limitations on the number of users who can effectively communicate with the base station. Intercell interference also contributes as a limiting factor is cell capacity.
Since this invention helps to eliminate interference from adjacent cells and selectively directs transmission and reception of signals from each mobile unit equipped with the invention to and from the base station, an increase in the number of users per cell is realized.
Moreover, the invention reduces the required transmit power for each mobile subscriber unit by providing an extended directed beam towards the base station.
Alternative physical embodiments of the antenna include a four element antenna wherein the three passive antenna elements are positioned at corners of an equilateral triangular plane and are arranged orthogonally and extend outward from that plane. The active antenna element is similarly situated but is located in the center of the triangle.
The passive antenna elements 701-705 are selectably operated in one of two modes: reflective mode and transmissive mode. A processor (not shown but described in reference to
In reflective mode, the passive antenna elements 701-705 are effectively elongated by being inductively coupled to ground. In transmissive mode, the passive antenna elements 701-705 are effectively shortened by being capacitively coupled to ground. The direction of a beam steered by the antenna apparatus 700, therefore, can be determined by knowing which passive antenna elements are in reflective mode and which are in transmissive mode. The direction of the beam extends to/from the active antenna element, projecting past the passive antenna elements in transmissive mode and. away from the passive antenna elements in reflective mode.
The antenna apparatus 700 includes a platform or housing 710 upon which the five passive antenna elements 701 through 705 and active antenna element 706 are mounted. Within the housing 710, the antenna apparatus 700 includes adjustable impedance components 711 through 715. For an embodiment having multiple active antenna elements 706, the antenna apparatus 700 includes components shown and described in
In a preferred embodiment, each passive antenna element 701 through 705 is disposed on the surface of the housing 710, as illustrated in the figure. In this preferred embodiment, the passive antenna elements 701, 702, 703, 704 and 705 are respectively positioned at locations corresponding to the radial edge of a circle, and the active antenna element 706 is positioned at a location corresponding to the center of the circle. The distance between each passive antenna elements 701 through 705 and the active antenna element 706 is great enough so that the phase relationship between a signal received by more than one element 701 through 706 will be somewhat out of phase with other elements that also receive the same signal, assuming the passive antenna elements 701 through 706 have the same impedance setting, which translates into phase setting, as determined by adjustable impedance components 711 through 715. That is, if the phase setting of each element 701 through 705 were the same, each element 701 through 705 would receive the signal somewhat out of phase with the other elements.
However, according to the operation of the antenna 700 in this invention, the selectable impedance components 711 through 715 are independently adjustable to affect the directionality of signals to be transmitted and/or received to or from the subscriber unit (i.e., laptop computer 150 in this example). By properly adjusting the phase for each passive antenna element 701 through 705 during signal transmission by the active antenna element 706, a composite beam is formed that may be positionally directed towards the base station 160. That is, the optimal phase setting for sending a reverse link signal 170 from the antenna apparatus 700 is a phase setting for each passive antenna element 701 through 705 that re-radiates RF energy to assist in creating a directional reverse link signal. The result is an antenna apparatus 700 which directs a stronger reverse link signal pattern in the direction of the intended receiver base station 160.
The phase settings used for re-radiating RF energy of transmission signals also cause the passive antenna elements 701 to 705 to allow the active antenna element 706 to optimally receive forward link signals 180 that are transmitted from the base station 160. Due to the programmable nature and the independent phase setting of each passive antenna element 701 through 705, only forward link signals 180 arriving from a direction that is more or less in the location of the base station 160 are optimally received. The passive antenna elements 701 through 705 naturally reject other signals that are not transmitted from a similar location as are the forward link signals. In other words, a directional antenna beam is formed by independently adjusting the phase of each passive antenna element 701 through 705.
The selectable impedance components 711 through 715 shift the phase of the reverse link signal in a manner consistent with re-radiating RF energy by an impedance setting associated with that particular selectable impedance component 711 through 715, respectively, as set by an impedance control input 730. In one embodiment, the impedance control input 730 is provided over a number of lines equal to the number of passive antenna elements, five, multiplied by the number of impedance states minus one for each of the selectable impedance components 711-715. For example, if the selectable impedance components 711-715 have two states, then there are five lines.
Alternatively, a serial encoding method of the states may be employed to reduce the number of control lines to one, which would then require appropriate decode circuitry to be used on the housing 710.
By shifting the phase of the re-radiated RF energy of the transmitted reverse link signals 170 from each element 701 through 705, certain portions of the transmitted signal 170 will be more in phase with other portions of the transmitted signal 170. In this manner, the portions of signals that are more in phase with each other will combine to form a strong composite beam for the reverse link signals 170. The amount of phase shift provided to each antenna element 101 through 105 through the use of the selectable impedance components 711 through 715, respectively, determines the direction in which the stronger composite beam will be transmitted, as described above in terms of reflectance and transmittance.
The phase settings, provided by the selectable impedance components 711 through 715, used for re-radiating RF signals from each passive antenna element 701 through 705, as noted above, provide a similar physical effect on a forward link frequency signal 180 that is received from the base station 160. That is, as each passive antenna element 701 through 705 re-radiates RF energy of a signal 180 from the base station 160 to the active antenna element 706, the respective received signals will initially be out of phase with each other due to the location of each passive antenna element 701 through 705 upon the housing 710. However, each received signal is phase-adjusted by the selectable impedance components 711 through 715. The adjustment brings each signal in phase with the other re-radiated signals 180. Accordingly, when each signal is received by the active antenna element 706, the composite received signal will be accurate and strong and in the direction of the base station 160.
To optimally set the impedance for each selectable impedance component 711 through 715 in the antenna apparatus 700, the selectable impedance components 711-715 control values are provided by the controller 140 (
The processor 140 thus determines an optimal phase setting for each passive antenna element 701 through 705 based on an optimized reception of a current pilot signal 190. The processor 140 then provides and sets the optimal impedance for each selectable impedance component 711 through 715. When the antenna apparatus 700 enters an active mode for transmission or reception of signals between the base station 160 and the laptop 150, the impedance settings of the adjustable impedance components 711 through 715 remain as set during the previous idle time period.
Before a detailed description of phase (i.e., impedance) setting computation as performed by the processor 140 is given, it should again be understood that the principles of the present invention are based in part on the observation that the location of the base station 160 in relation to any one mobile subscriber unit (i.e., laptop 150) is approximately circumferential in nature. That is, if a circle were drawn around a mobile subscriber unit and different locations are assumed to have a minimum of one degree of granularity between any two locations, the base station 160 can be located at any of a number of different possible angular locations. Assuming accuracy to one degree, for example, there are 360 different possible phase setting combinations that exist for an antenna 100. Each phase setting combination can be thought of as a set of five impedance values, one for each selectable impedance component 711-715 electrically connected to respective passive antenna elements 701 through 705.
There are, in general, at least two different approaches to finding the optimized impedance values. In the first approach, the controller 140 performs a type of optimized search in which all possible impedance setting combinations are tried. For each impedance setting (in this case, for each one of the 360 angular settings), five precalculated impedance values are read, such as from memory storage locations in the controller 140, and then applied to the respective selectable impedance components 711 through 715. The response of the receiver 130 is then detected by the controller 140. After testing all possible angles, the one having the best receiver response, such as measured by maximum signal to noise ratio (e.g., the ratio of energy per bit, Eb, or energy per chip, Ec, to total interference, Io), is used.
In a second approach, each impedance value is individually determined by allowing it to vary while the other impedance values are held constant. This perturbational approach iteratively arrives at an optimum value for each of the five impedance settings.
The switch 801a is a single-pole, double-throw switch controlled by a signal on a control line 820a. When the signal on the control line 820a is in a first state (e.g., digital “one”), the switch 801a electrically couples the passive antenna element 701 to the capacitive load 805a. The capacitive load makes the passive antenna element 701 effectively shorter. When the signal on the control line 820a is in a second state (e.g., digital “zero”), the switch 801a electrically couples the passive antenna element 701 to the inductive load 810a, which makes the passive antenna element 701 effectively taller, and, therefore, reflective.
The switch 801b is a single-pole, multiple-throw switch controlled by binary-coded decimal (BCD) signals on four control lines 820b. The signal on the four control lines 820b command a pole 803 of the switch 801 b to electrically connect the passive antenna element 701 to 1-of-16 different impedance components. As shown, there are only nine impedance components provided for coupling to the passive antenna element 701.
The selectable impedance components include capacitive elements 805b, inductive elements 810b, and delay line elements 815. Each of the impedance components is electrically disposed between the switch 801b and the ground plane 740.
In this embodiment, the capacitive elements 805b include three capacitors: C1, C2, and C3. Each capacitor has a different capacitance to cause the passive antenna element 701 to have a different transmissibility when connected to the passive antenna element 701. For example, the capacitive elements 805b may be of an order of magnitude a part in capacitance value from one another.
Similarly, the inductive elements 810b include three inductors: L1, L2, and L3. The inductive elements 810b may have inductance values an order of magnitude apart from one another to provide different reflectivities for the passive antenna element 701 when connected to the passive element 701.
Similarly, the delay line elements 815 include three different lines: D1, D2, and D3. The delay line elements 815 may be sized to create a phase shift of the signal re-radiated by the passive antenna element 701 in, say, thirty degree increments.
In an alternative embodiment, the switch 801b may be a double-pole, double-throw switch to provide different combinations of impedances coupled to the passive antenna element 701 to provide various combinations of impedances. In this way, the passive antenna element 701 can be used to re-radiate RF energy to the active antenna element 706 with various phase angles to allow the antenna apparatus 700 to provide a directive beam at various angles. In one case, the controller 140 (
Alternative technology embodiments of the switch 801b are possible. For example, the switch 801b may be composed of multiple. single-pole, single-throw switches in various combinations. The switch 801b may also be composed of solid-state switches, such as GaAs switches or pin diodes and controlled in a typical manner. Such a switch may conceivably include selectable impedance component characteristics to eliminate separate impedance or delay line components. Another embodiment includes Micro-Electro Machined Switches (MEMS), which act as a mechanical switch, but have very fast response times and an extremely small profile.
In this configuration, two passive antenna elements 701, 705 are in the reflective mode, and the other passive antenna elements 702-704 are in the transmissive mode. The directive beam 900 resulting from this configuration extends from the active antenna element directly over the central of the three passive antenna elements 702-704 in the transmissive mode. It is assumed that the passive antenna elements 701, 705 in reflective mode are electrically connected to selectable impedance components having the same inductance values, and the passive antenna elements 702-704 in the transmissive mode are electrically connected to selectable impedance components having the same capacitance values. It should be understood that selecting different angles of the directive beam 900 can be provided by different re-radiating phase angles by the passive antenna elements 701-705, such as selecting of one of the passive antenna elements 702-704 in the transmissive mode to have a different capacitance value than the other two.
Another mechanical adjustment that can be made to the passive antenna elements is through the use of adjustability slots 1010. The adjustability slots 1010 allows the passive antenna elements 701-705 to be manually moved radially inward and outward from the active antenna element 706. Alternatively, the adjustability slot could be a series of threaded screw mounts to which the passive antenna elements 701-705 are capable of being connected. In addition, multiple rings of passive antenna elements, optionally staggered, could be provided, though efficiency of the mutual coupling outwardly decreases. By varying the spacing between the passive elements 701-705 and central active antenna element 706, the angle of the beam produced by the antenna apparatus 700 can be changed as desired.
Yet another manual adjustment that can be made to the passive antenna elements 701-705 is the addition of a tubular coupling that can be placed on top of the passive elements 701-705. As shown, tubular couplings 1015 are placed on top of passive antenna elements 701 and 705. The tubular couplings 1015 increase the diameter of the passive antenna elements, making the passive antenna elements re-radiate differently from the passive antenna elements without the tubular couplings 1015. It should be understood that the tubular couplings 1015 may, in fact, be thicker, replaceable, passive antenna elements. In either case, the directive beam 900 (
It should also be understood that the manual adjustments (i.e., 1005, 1010, 1015) can be (i) combined in various ways and applied to only subsets of the passive antenna elements 701-705 and (ii) combined with the electrical selectable impedance components 711-715 in a variety of configurations. Both combinations produce various beam patterns and angles by the antenna apparatus 700. Instructions for making such manual adjustments may be provided via a display on the computer screen of the computer 150 (
If a directional beam is to be generated and manual impedance selection is to be performed, the process 1100 continues to step 1125 for a user of the subscriber unit to manually adjust the antenna assemblage of the antenna apparatus 700. In this case, again, the processor 140 (
If, in step 1115, the process determines that an omni-directional beam pattern is desired, then, in step 1135, omni-directional mode is provided. For the antenna apparatus 700 to provide omni-directional mode, the passive antenna elements 701-705 are coupled to respective selectable impedance components 711-715 having essentially the same capacitance values so that the active antenna element 706 can transmit and receive signals “over” the passive antenna elements 706. Alternatively, a mechanical configuration providing omni-directional mode may be provided by the user, where, for example the active antenna element 706 is telescoped upward to provide an antenna element sufficiently taller than the passive antenna elements 701-705. The process 1100 ends in step 1140.
In step 1201, the controller 140 determines that the idle mode has been entered, such as by detecting certain forward link signals 180. Step 1202 then begins a loop that will execute once for each possible angle or location at which the base station 160 may be located. In the preferred embodiment, this loop is executed 360 times. Step 1203 then programs each selectable impedance component 711 through 715 with an impedance setting corresponding to the first location (i.e., angle 0) setting. The impedance settings may, for example, be precalculated and stored in a table, with five selectable impedance component settings for each possible angle corresponding to the five elements of the array. In other words, step 1203 programs impedance settings for a first angle, which may be conceptualized as angle 0 in a 360 degree circle surrounding the mobile subscriber unit 60. Step 1204 then measures the received pilot signal 190, as received by the active antenna element 706. The measurement in step 1204 reflects, in part, how well each passive antenna element 701 through 705 re-radiated the received pilot signal 190 based upon the current set of programmed impedance settings applied in step 1203. Step 1264 saves the measurement as a received signal metric value. The metric may, for example, be a link quality metric as bit error rate or noise energy level per chip (Ec/No).
Step 1205 then returns processing to step 1202 to program the selectable impedance components for the next set of impedance settings. Steps 1202 through 1205 repeat until all 360 sets of phase settings have been programmed into selectable impedance components 711 through 715 (step 1203) and a measurement has been taken of the received pilot signal 190 for each of these settings (step 1204). After step 1205 determines there are no more sets of impedance settings, step 1206 determines the best set of impedance settings, as determined by which settings produced the strongest receive signal metric value. Step 1207 then programs the selectable impedance components 711 through 715 with the set of impedance settings that was determined to produce this best result.
During long periods of idle time, step 1208 is executed, which repeats the process periodically. Step 1208 accounts for the fact that the antenna apparatus 700 might be moved and re-oriented during idle periods, thus affecting the direction and orientation of the base station in relation to the antenna apparatus 700.
In addition, the antenna apparatus 700 may be optimized during transmission. In this manner, steps 1201 through 1208 continuously update and set optimal impedance settings for each passive antenna element 701 through 705. It should be understood that a second process for setting phases of a phased array antenna (e.g., antenna elements 101-105,
In step 1301, one of the passive antenna elements 701 through 705 is selected. In step 1302, the phase settings of the four remaining passive antenna elements, via the respective selectable impedance components not selected in step 1301, are fixed in value. Step 1303 then varies the impedance setting of the selectable impedance component associated with the non-fixed passive antenna element selected in step 1301 until the setting that maximizes the pilot signal metric is determined. Then, the process repeats by returning to step 1301, where the previously selected passive antenna element is fixed to this optimum phase and the impedance setting corresponding to one of the other passive antenna elements is varied. The process continues until each passive antenna element is configured with an optimal setting. As the process iterates, the impedance settings of each selectable impedance component, providing phase adjustment for an associated passive antenna element, converge to an optimum setting.
The algorithm fixes a value for four of the five unknown, optimum impedance settings (i.e., weights) W[i], e.g. W[2] through W[5]. The algorithm perturbs the system and observes the response, adapting to find the optimum value for the unfixed impedance value, e.g. W[1]. The measured link quality metric, in this case Ec /Io, is fed to a first gain block G1. Again input G is fed to a second gain block G2. A first fast “clock” date value, CLK1, which alternates from a value of “1” to a value of “−1” is inverted by 11 and fed to a first multiplier M1. The other input of multiplier M1 is fed by the gain block G2.
The output of M1 is fed to a second multiplier M2 together with the output of G1. An integrator N1 measures an average level and provides this to the latch L. A slow clock CLK2, typically alternating at a rate which varies between “1 ” and “0” and is much slower than CLKI, by at least 100 times, drives the latch “clock” C. The output of the latch L is summed by summation block S with the non-inverted output of M2. The result, W[i], is a value which tends to seek a localized minima of the function.
The process shown in
Alternatively, instead of varying an impedance assigned to each passive antenna element 701 through 705, the impedance setting corresponding to each passive antenna element can be stored in a table of vectors, each vector having assignments corresponding to the five passive antenna elements 701 through 705. The five values in each vector can be computed based upon the angle of arrival of the received pilot signal. That is, the impedance values for each selectable impedance component corresponding to each passive antenna element are set according to the direction in which the base station is located in relation to the mobile subscriber unit. The angle of arrival can be used as a value to lookup the proper vector of weights (and/or impedance settings) in the table. By using a table with vectors, only the single angle of arrival calculation needs to be performed to properly set the impedance settings corresponding to each passive antenna element 701 through 705.
The manufacturing process 1500 can be modified in various ways. For example, in step 1515, the manufacturing process 1500 can include attaching at least one active antenna element to the circuit board. Further, multiple types of selectable impedance components can be connected to the circuit board. It should be understood that various types of selectable impedance components can be connected to the circuit board; for example, the selectable impedance components may be printed on the circuit board on the same layer as the ground plane 740, attached as discrete elements to the circuit board, or wave soldered to the circuit board in the form of a “chip” that includes discrete components (i.e. inductors, capacitors, delay lines, varactors, etc.).
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described specifically herein. For example, there can be alternative mechanisms to determining the proper phase for each passive element, such as storing impedance setting values in a linked list or a database instead of a table. Moreover, those skilled in the art of radio frequency measurement understand there are various ways to detect the origination of a signal, such as the received pilot signal. These mechanisms for determining the location of signal origination are meant to be contemplated for use by this invention. Once the location is known, the proper impedance setting for passive antenna elements may be performed. Such equivalents are intended to be encompassed in the scope of the claims.
This application is a Divisional of U.S. application Ser. No. 10/744,912, filed Dec. 23, 2003, entitled “Adaptive Antenna for Use in Wireless Communication Systems,” which is a Continuation-In-Part of co-pending U.S. application Ser. No. 10/441,977 filed May 20, 2003, entitled “Adaptive Antenna for Use in Wireless Communication Systems,” which is a Divisional of U.S. application Ser. No. 09/859,001, filed on May 16, 2001, now U.S. Pat. No. 6,600,456, issued Jul. 29, 2003, which claims the benefit of U.S. Provisional Application No. 60/234,485, filed on Sep. 22, 2000, and is a Continuation-In-Part of U.S. patent application Ser. No. 09/579,084 filed on May 25, 2000, now U.S. Pat. No. 6,304,215, which is a Divisional of U.S. application Ser. No. 09/210,117, filed on Dec. 11, 1998, now issued U.S. Pat. No. 6,100,843, which is a continuation of U.S. patent application Ser. No. 09/157,736 filed on Sep. 21, 1998, now abandoned. The entire teachings of the above applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60234485 | Sep 2000 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10744912 | Dec 2003 | US |
| Child | 11332901 | Jan 2006 | US |
| Parent | 09859001 | May 2001 | US |
| Child | 10441977 | May 2003 | US |
| Parent | 09210117 | Dec 1998 | US |
| Child | 09579084 | May 2000 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09157736 | Sep 1998 | US |
| Child | 09210117 | Dec 1998 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10441977 | May 2003 | US |
| Child | 10744912 | Dec 2003 | US |
| Parent | 09579084 | May 2000 | US |
| Child | 10441977 | May 2003 | US |
