Patent Application
20070087770
The present invention relates generally to the regulation of electromagnetic waves, and more particularly to transmission power control in a wireless communication system.
Wireless communication systems, including cellular telephone networks, are the primary means of electronic communication for millions of users. User demand has driven the market for wireless devices to become smaller, lighter, more powerful and adaptable for multi-mode and multi-band usage. For example, software-defined radio (SDR) systems have been developed for wireless communication in which a transmitter signal is generated by a computer program using a selected modulation type. An SDR receiver uses a matching computer program to recover the signal intelligence. Despite such advances, the rapid growth in wireless communication traffic, as well as the introduction of advanced multimedia wireless capabilities, has created challenges for system designers in the area of transmission power control.
“Transmission power” generally describes the power for transmitting a signal. As used herein, a “signal” is defined as an electromagnetic wave capable of having intelligence imposed thereon. The term signal may also include more than one signal, as a device may transmit a plurality of related signals during a particular communication session.
Transmission power consumes a large part of the battery capacity in a wireless device. Put simply, the more power required for a device to transmit, the shorter the amount of time the device battery will last. Therefore, transmission power provides a limit to the number of devices that can communicate over a system at a given time because, generally, more traffic will increase the amount of power necessary for a device to transmit and will drain battery power. However, designers can increase system capacity and the battery life of wireless devices by actively adjusting transmission power relative to receivers in a network. The goal of transmission power control is to improve link quality of service while overcoming the deleterious effects of signal fade, multi-path signal scattering and other forms of environmental interference. As such, the challenge for designers is to minimize the transmission power necessary for a successful communication link in order to preserve battery life while maintaining an acceptable signal to noise ratio and bit error rate. While various transmission power control techniques are known in the art for 1 G (analog voice) and 2 G (digital voice) wireless communication systems, these methods have proven to be less effective by measures of cost, packaging and efficiency for “wideband” 2.5 G and 3 G (high speed voice/video/data) wireless systems.
In particular, transmission power control is important for code division multiple access (CDMA) based systems. CDMA signals are distinguished only by a unique code that is added to each signal before transmission. The CDMA method contrasts with other communication modes that use time, frequency, phase or other differences to distinguish between signals. Therefore, CDMA transmissions rely on transmission power levels for the coded signals to be clearly distinguishable and thus, present several power control challenges. For example, a “near and far” problem exists when signals that are nearer to a receiving terminal are stronger than signals that are relatively far away from the receiving terminal. In such an instance, the weak “far” received signals tend to be jammed by strong “near” signals. In another example, a similar phenomenon occurs in the instance where a signal is transmitted near to a receiving terminal, but its transmission is obstructed by environmental conditions. Although the signal source is relatively close to the receiving terminal, scattering, reflection, fading or other attenuation of the received signal will result in a weaker, distorted or dropped transmission link.
Although advanced network transmission power control presents new challenges for system designers, many high-efficiency power transmission technologies have been developed recently, including digital polar modulation and linear amplifier with no linear components (LINC) systems. Digital polar modulation allows for a more accurate reproduction of an input signal by separating the signal into its amplitude and phase components. The separated phase component is amplified by a highly non-linear (efficient) means of multiple control variables for gain control over a wide dynamic range. The amplitude component is later added back to the phase component for a relatively accurate reproduction of the input signal versus prior amplification methods. As such, digital polar modulation reduces the transmission power necessary for an efficient and successful link and as a result, increases system capacity.
Fast response, low power, low current consumption transmission power control is required to fully realize the benefits of highly efficient transmission technologies like digital polar modulation. Therefore, what is needed in the art is an improved transmission power control method adaptable for multi-mode, multi-band, SDR communication systems such as those that use digital polar modulation for wireless transmissions in “real world” environmental conditions.
Embodiments of the invention include methods and apparatuses for transmission power control in a wireless communication system. Various embodiments of the invention include a method of power control for a wireless terminal comprising receiving at least one input parameter indicative of a transmission power level, generating a control parameter based on the at least one parameter and regulating an output transmission power level of the wireless terminal based on the control parameter.
Other embodiments of the invention include an apparatus for power control in a wireless terminal. A receiver receives at least one input parameter indicative of a transmission power level. A processor generates a control parameter based on the at least one input parameter and a controller regulates an output transmission power level of the wireless terminal based on the control parameter.
Still other embodiments include a computer-readable medium having computer executable instructions for determining at least one parameter indicative of a power level of a transmitting wireless terminal, generating a control parameter based on the at least one parameter, and regulating an output transmission power level of a receiving wireless terminal based on the control parameter.
A more complete appreciation of the invention, and many of the attendant features and advantages thereof, will be readily obtained as the same become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein
Embodiments of the invention include apparatuses, methods and articles of manufacture adapted for transmission power control in a wireless communication system. As will be described further below, the invention regulates the output transmission power of a wireless terminal utilizing any of a variety of measures, including estimation from previous transmission power level information. As such, the invention is suitable for regulating the output transmission power level of a wireless terminal in a wireless communication system operating in a “real world” environment.
Before describing the invention in detail, certain terms should be defined for a more complete understanding of this description. As used herein, the term “signal” should be understood to include an electromagnetic wave capable of having intelligence impressed thereon. It should be further understood that a signal may include one or more signals such as, for example, when a device transmits a plurality of related signals in a given communication session.
The term “wireless terminal” as used herein includes any device that may transmit and/or receive a wireless signal. For example, a wireless terminal may include a mobile device such as a radiotelephone handset, a stationary device such as a base station or a relay device which may include one or more mobile or stationary devices. In general, a wireless terminal may communicate with one or more other terminals by transmitting a signal utilizing a wireless transmission mode. The invention is useful for a variety of wireless transmission modes which are currently known, or may in the future be known. For example and not limitation, wireless transmission modes contemplated herein include code division multiple access (CDMA), wide-band CDMA (W-CDMA), CDMA2000, time division multiple access (TDMA), global system for mobile communications/general packet radio service (GSM/GPRS), enhanced data GSM environment (EDGE), third generation GSM (3GSM), integrated digital enhanced network (iDEN), wireless local area network (WLAN), Bluetooth®, Wi-Fi® or any combination thereof. These wireless transmission modes may operate at multiple bandwidths including, for example, the GSM/GPRS 800 MHz and 1900 MHz frequency bandwidths in the United States and the international GSM/GPRS 900 MHz and 1800 MHz frequency bandwidths. In various embodiments, the wireless terminals may be software-defined radios (SDRs) wherein transmitter modulation is performed by a computer program with selectable multi-mode and/or multi-band settings to send a signal. A receiver SDR performs demodulation using a matching computer program to receive the signal intelligence.
In the embodiments described herein, the invention is oriented to compensate for power fading sources and their characteristics. However, the invention is adaptable to compensate for any of a variety of environmental conditions including, but not limited to, signal scattering, reflection, fading, shadowing, interference and/or any combination thereof. In addition, the approach proposed in the present invention can also be extended to multiple input and multiple output (MIMO) antenna systems.
In one embodiment, the invention uses a parallel multi-input and multi-control variable system architecture to control the output power of a transmitter. Generally, the inputs are classified multidimensional measures of the difference between an actual power level and a desired power level at the related receivers in a network, i.e., the required power adjustments. The multi-control variables may be, for example, the multi-gain control ports of a transmitter. A digital programmable processor generates the executive commands for the multi-control variables using, for example, a power control program, divisive input measures and/or commands.
The multi-control variables provide large flexibility for the linear transmission systems that do not use linear amplification components, such as digital polar transmitters and “LINC” (linear amplifier with no linear components) systems, where the amplifiers may operate in a wide gain control range and achieve minimum current consumption over the entire operation dynamic range. In summary, the system provides fast power control convergence, low transmitted power, and low current consumption without requiring complicated high power, high dynamic range power control circuitry.
Turning now to the various embodiments of the invention,
In one embodiment, the input register 12 includes a received power register 18 for recording received signal power values, an interference correction register 20 for recording interference correction values from the network, a power control register 22 for received power control commands, and a transmitted power register 24 for recording measurements of transmitted power. An antenna 20 is coupled to the receive gain controller 26, which in one embodiment may include a receive amplifier (not shown) to amplify an incoming signal. The output of the receive gain controller 26 is coupled to the received power register 18 and a mobile receive digital module 28. A mobile transmission digital module 30 is shown to be coupled to the processor 14 as well as to the output gain controller 16. The output gain controller 16 may include a transmitter amplifier to amplify an outgoing signal. The output gain controller 16 is coupled to the antenna 20 for transmitting a signal based on the regulated output transmission power level.
In one embodiment, the control approach is a multi-input and multi-control variable approach. A plurality of input parameters 32, 34, 36, 38, 40 of the processor 14 are all available resources for estimating output transmission power control adjustments from measures of both wireless terminal and network feedback. The input parameters 32, 34, 36, 38, 40 are classified based on their respective characteristics. The inputs and control variables are independent in time and gain range. The control variables set the gain. For example, the gain controller 16 may set the gain to compensate for a class of power fading sources with classified characteristics that will specify the resolution, response time, and power range.
The processor 14 may include software and/or hardware for receiving the power control input parameters 32, 34, 36, 38, 40 and generating commands that are outputted 42 to the gain controller 16 to regulate the output transmission power. The output of the processor 14 is based on the input parameters 32, 34, 36, 38, 40, their various characteristics, the various estimation criteria and control rules.
Various embodiments of the invention may be represented mathematically. As illustrated below, the mapping from power control input parameters and output transmission power are memory-less, non-linear functions which can be expressed in vector format:
X=Φ(X, U, V, t) P=Ψ(X, t) (1)
Where, X=(x1, x2, . . . xn)T is the state vector of the transmitter signal strength. U=(u1, u2, . . . um)T is the control variable vector, V=(v1, v2, . . . v1])T the signal vector. P=(p1, p2, . . . pk)T is the output power vector, Φ and Ψ are mapping matrix functions, as will be known to those skilled in the art, and t is time.
The control variable U is the output of the processor 14:
U=G(S, X, θ, N) (2)
Where S=(s1, s2, . . . si)T is the vector of power control inputs. The parameter G is the power control function that maps S to U based on power control rules through power control algorithms in the command generator. θ is the link channel parameter vector, and N is the noise vector. It should be observed that the circuit could be operated in non-linear mode. The control variable U depends on X. The link channel parameter θ is partially based on previous link channel information and partially adaptively updated through the network and/or wireless device. The power control function G is selected so that both the current drawn of the transmitter and the transmitted power at receiver are minimized while maintaining an acceptable signal to noise ratio and bit error rate.
A block diagram illustrating the operation of the processor 14 is illustrated in
The processor 14 utilizes the inputs from the digital amplitude profile adjustment 40 and the digital amplitude corrections 202 to generate a digital amplitude profile 204 for a transmission output signal. Likewise, the processor utilizes the input parameters 32, 34, 36, 38 and the frequency and temperature corrections 200 to generate gain control settings for each of the gain control variables of the output gain controller 16. For example, the non-linear phase component of the output gain controller 16 may include n gain control variables with variable ‘1’ being the most significant gain control bit and variable ‘n’ being the least significant. In such a case, the processor 14 may generate each gain control bit utilizing a predetermined rule that may be the same or different than the rules governing the other bits. As such, at least one of the input parameters and corrections 32, 34, 36, 38, 40, 200, 202 subject to the rule for bit ‘1’ may be utilized at block 206 to generate transmission gain control variable ‘1’ 208. Likewise, the input parameters and corrections subject to the rule for bit ‘n’ may be utilized at block 210 to generate transmission gain control variable ‘n’ 212.
If the processor 14 determines that fast performance is not required based on the feedback inputs from the network at block 304 or if the estimated received power and/or interference correction are not within acceptable parameters in blocks 310 and 312, the processor wil determine whether the power control adjustment is too slow at block 322. If the processor 14 determines that the power control adjustment is too slow, the processor increases the power control intervals at block 324. For example, the processor 14 may increase the frequency of feedback sampling periods in which it can generate power control commands 326. If the processor 14 determines that the adjustment is not too slow, the processor 14 will maintain the frequency of feedback sampling periods and generate power control commands 326 at the same rate. For example, “coarse” control rules, as will be known to those skilled in the art, may be applied to regulate gain when slow fading is detected.
The initial RF power from the VCO 410 is adjustable in high and low modes with a 12 dB dynamic range. In one embodiment, the reference gain of the digital amplitude restoration amplifiers 412 gain is controlled through the reference bias settings.
The gain controllers 402, 404 are core power control components that are independently controlled to execute divisive and adaptive control algorithms. In one embodiment, the overall system provides more than 80 dB dynamic range and is adaptable to transmission power control needs for wireless communication networks, such as, for example, CDMA2K, WCDMA, TDMA, GSM/GPRS, EDGE, 3GSM, WLAN, Wi-Fi® and Bluetooth® networks.
As such, the invention provides fast response, low power, low current consumption transmission power control for a variety of power trasmission technologies, including digital polar modulation. It will be appreciated that the invention provides transmission power control for wireless devices to facilitate improved wireless transmissions in various real world environmental conditions.
Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.
