Patent Application
20090034438
The invention relates to systems and methods for wireless communications networks, especially flexible broadband wireless systems.
Modern cellular networks are following a general trend of evolution towards higher transfer rates and better support for mobility. In this context, OFDM (Orthogonal Frequency Division Multiplexing) techniques have an excellent potential since they can achieve a wide range of transfer rates in a variety of physical environments. Therefore, a number of modern standards have adapted OFDM-based physical layers, e.g. WIFI, WIMAX, 3G LTE and Flash OFDM. While existing standards-based OFDM systems have some degree of flexibility, every system has a set of standard-specific parameters that are mandatory and that render the system suitable for only a predefined domain of operating conditions, e.g. in terms of data rates, ranges, mobility. A channel cannot be established if those conditions are not met.
EP-869647-A2 discloses a scaleable OFDM system comprising control circuitry for scaling various operating parameters and characteristics of an OFDM channel so as to support a variety of services, in a variety of environments, indoor as well as outdoor and in radio channels with differing bandwidths. In operation, a receiving station sends a request for particular operating parameters through its OFDM transmitter to the OFDM receiver of a transmitting station. Dynamic control circuitry at the transmitting station dynamically scales the operating parameters, such as data rate between the stations. It follows from this mode of operation that operating parameters can only be scaled after a remote terminal has initially synchronized with a base station. Therefore, the initial access of the remote terminal to the radio network can only be achieved by using a predefined physical OFDM profile. When synchronization of the OFDM channel is absent or lost, the OFDM system always starts or re-starts with operating parameters corresponding to low data rate between the base station and a remote unit.
For a wireless receiver to synchronize with a transmitter, it must learn or detect the characteristics of the channel used by the transmitter. While a radio receiver can typically scan a predefined frequency band until it detects the carrier frequency used by the transmitter, such an approach is not workable for wireless systems having a high number of degrees of freedom. Indeed, the time needed for a receiver to scan the entire multidimensional space of possible operating points, until synchronization with the transmitter is achieved, would be unreasonable.
According to one aspect, it is an object of the invention to provide a flexible wireless communication system that can operate in a variety of situations, e.g. regarding number of users, environmental conditions, service requirements. According to another aspect, it is an object of the invention to provide a flexible wireless communication system that enables a broadband transmitter and a broadband receiver to synchronize in a variety of situations, e.g. regarding number of users, environmental conditions, service requirements. According to still another aspect, it is an object of the invention to provide a flexible wireless communication device adapted to dynamically change its operating parameters without loosing connectivity with other communication devices.
According to the invention, these objects are achieved by a method for establishing a parameterized wireless communication channel between at least two communication devices, comprising the steps of: communicating physical profile data between a first communication device
and a second communication device,
and configuring a parameterized wireless communication means in the first and second communication devices in accordance with the physical profile data, so as to establish a traffic communication channel between the first and second communication devices,
wherein the physical profile data is communicated on a wireless spread spectrum channel having an operational frequency range that overlaps an operational frequency range of the traffic communication channel.
According to embodiments of the method, the following features can be taken individually or in combination:
The invention provides also a wireless communication device comprising a spread spectrum communication means for transmitting and/or receiving physical profile data on a wireless spread spectrum channel, a parameterized communication means for transmitting and/or receiving data on a parameterized traffic communication channel, and a physical profile management means for configuring the parameterized communication means in accordance with physical profile data transmitted or received by the spread spectrum communication means.
In embodiments of the wireless communication device, the spread spectrum communication module includes at least one of a spread spectrum wireless transmitter, a spread spectrum wireless receiver and a spread spectrum wireless transceiver. Similarly, the traffic communication module includes at least one of an orthogonal frequency division multiplexing wireless transmitter, an orthogonal frequency division multiplexing wireless receiver and an orthogonal frequency division multiplexing wireless transceiver.
According to embodiments of the wireless communication device, the following features can be taken individually or in combination:
The invention provides also a base station comprising the wireless communication device, wherein the spread spectrum communication means is capable of transmitting the physical profile data in broadcast mode in at least one cell.
In an embodiment, the spread spectrum communication means is capable of transmitting a plurality of physical profile data sets allocated to a corresponding plurality of wireless terminals on the spread spectrum channel.
The invention provides also a wireless terminal comprising the communication device, wherein the spread spectrum communication means is capable of receiving the physical profile data on the spread spectrum channel.
The wireless terminal can be fixed or mobile.
In an embodiment, the spread spectrum communication means is capable of sending physical profile request data on the spread spectrum channel for causing a base station to transmit physical profile data in response to said physical profile request data.
In an embodiment, the physical profile request data comprise a description of a physical condition of the terminal, such as velocity or position or other.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, by way of example, with reference to the drawings.
Below will be described several embodiments of a wireless communication system that comprises a main system for implementing a traffic communication channel, e.g. OFDM or other and a secondary system for implementing a secondary channel, e.g. spread spectrum or other. The secondary channel overlaps with the traffic channel in the frequency domain, yet it does not adversely affect the operation of the main system. The secondary system serves to provide information to a configuration system for configuring the main system.
Referring to
According to embodiments, OFDM communication module 11 or 21 includes a radio receiver and an OFDM baseband module for reception of data, or a radio transmitter and an OFDM baseband module for transmission of data, or both. According to embodiments, spread spectrum communication module 12 or 22 includes a radio receiver and a spread spectrum baseband module for reception of data, or a radio transmitter and a spread spectrum baseband module for transmission of data, or both. In embodiments where one or both of the channels 2 and 4 are bidirectional, the duplexing technique can be either time division duplexing or frequency division duplexing. The OFDM communication module 11 or 21 and spread spectrum communication module 12 or 22 of the same communication device 10 or 20 may share some components, e.g. a shared radio front-end as will be explained below.
The OFDM communication modules 11 and 21 are implemented as flexible modules that include dynamically configurable or programmable components for dynamically changing at least one operating parameter of the OFDM communication channel 2. For example, the flexible OFDM communication modules 11 and 21 can be implemented using technology known as software-defined radios. Each communication device 10, 20 also comprises an OFDM management module 13, 23 for controlling the configuration of the OFDM communication modules 11 or 21 as a function of the OFDM operating parameters to be applied, as shown by arrows 17 and 18.
Communication devices 10 and 20 use the spread spectrum channel 4 as a management channel for exchanging instructions relating to the operating parameters to be applied for establishing the OFDM channel 2. The spread spectrum channel 4 serves to communicate some or all of the operating parameters that are necessary for establishing the OFDM channel 2. According to one embodiment, the OFDM management modules 13 and 23 cooperate in a master/slave relationship, i.e. one of the communication devices 10 and 20 has mastership over the other communication device and uses the spread spectrum channel 4 for communicating the operating parameters to the other communication device. Mastership with respect to OFDM channel configuration can be set permanently or dynamically between the communication devices 10 and 20. According to another embodiment, the OFDM management modules 13 and 23 are capable of negotiating over the spread spectrum channel 4 to determine the operating parameters to be applied to the OFDM channel 2.
In one embodiment, the spread spectrum channel 4 is a static, predefined channel the parameters of which are preset or built-in in the spread spectrum communication modules 12 and 22. For example, the center frequency and the spreading sequence or frequency hopping sequence can be predefined and preconfigured in the communication devices 10 and 20, as well as in other communication devices, e.g. a plurality of wireless terminals. In another embodiment, the communication devices 10 and 20 are capable of negotiating some parameters of the spread spectrum channel 4. However, the most basic physical parameters of the spread spectrum channel 4 are preferably preset so that the spread spectrum communication modules 12 and 22 can always synchronize at the physical level without having to rely on an external source of information.
In an embodiment, the spread spectrum communication module comprises a data repository with a list of predefined profiles stored therein, e.g. a list of spreading sequences. In order to synchronize with the other communication device, the spread spectrum communication module tries out the profiles one after the other.
In a preferred embodiment, the spread spectrum channel 4 has an operational frequency band that overlaps at least part of an operational frequency band of the OFDM channel 2. The processing gain of the spread spectrum channel 4, i.e. the ratio of the data rate to the symbol rate, is set sufficiently high so that the spread spectrum channel can be received by the spread spectrum communication module 12 or 22, yet not degrade the performance of the OFDM channel 2. For example, a processing gain of 500 can be obtained with a 10 kbps data flow transmitted in a 5 MHz channel. The processing gain is related to the length of the spreading sequence.
Due to the very nature of spread spectrum signals, the spread spectrum channel 4 can transport data between the communication devices 10 and 20 with a spectral density of power very substantially lower than the density of power of the OFDM channel 2 in the operational frequency band of interest. This is illustrated in
In a preferred embodiment, the OFDM channel is used with a multiple access scheme known as OFDMA or Scalable OFDMA. In this case, in a given time slot, several group of subcarriers are allocated to different terminals. In the present specification, OFDM encompasses any waveform based on orthogonal subcarriers.
The operating parameters that are transmitted on the spread spectrum channel 4 can be of various types. Examples of operating parameters relevant to OFDM or OFDMA channels can be found in IEEE Standard for Local and Metropolitan area networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE Std 802.16-2004. A static, predefined spread spectrum channel is especially suitable for communicating a set of physical parameters that are fundamental to the definition of the OFDM channel. Fundamental here means that lack of prior knowledge of those physical parameters would make it very hard or impossible for an OFDM receiver to detect and synchronize with an OFDM transmitter that uses those physical parameters. Below is an illustrative, non-limitative list of such physical parameters:
OFDM channel bandwidth, Number of sub-carriers, sub-carrier frequency, sub-carrier spacing, identification of data sub-carriers, identification of pilot sub-carriers, identification of null subcarriers, identification of sub-carrier groups (or subchannels, segments, bins, clusters, bands), Sub-channel rotation scheme, frame duration, Symbol duration, sampling frequency, Guard interval, cyclic prefix duration, FEC code type, FEC coding rate, Data randomization related parameters, Data interleaving parameters.
Other operating parameters which can be communicated and potentially negotiated on the spread spectrum channel are: Center carrier frequency, Channel number, Permutation formula, Duplexing-related parameters, duplexing method FDD parameters, Downlink carrier frequency, uplink carrier frequency, TDD parameters, Downlink transmission period, uplink transmission period, transition gap, Synchronization information, Timers, Burst size, Baseband processing parameters, Symbol rate, Modulation rate, Modulation type, Number of bits per symbol, Repetition coding, Ranging parameters, Ranging method, Ranging channel, Ranging code, Transmit diversity scheme, Beam selection, Power-related parameters, maximum transmission power, power boosting, power control method, power adjustment rule, thresholds of all kinds, security related parameters, ciphering method, encryption method, security association, spreading parameters, sequence generator seed and others.
Parameters can be communicated on the spread spectrum channel 4 in various manners, i.e. explicitly or implicitly. A message communicated on the spread spectrum channel 4 can include physical values for corresponding physical parameters, or abstract identifiers, e.g. profile numbers referring to a predefined physical profile, i.e. a predefined physical parameter value or set of physical parameter values. Predefined physical profiles can be stored in any suitable data repository in the communication devices 10 and 20, e.g. a non-volatile memory.
In a preferred embodiment, the communication device 10 or 20 can be implemented with a shared radio front-end.
In embodiments, the communication system 1 is a point-to-multipoint OFDM system comprising at least one base station and a plurality of wireless terminals. Such an embodiment is schematically illustrated in
If the GSM system is active, the spectrum management module 56 allocates a first bandwidth value to the OFDM management module 55. The OFDM management module 55 determines and applies a set of operating parameters that constrains the OFDM channel 2 within that bandwidth. This situation is shown in
There are several ways of setting the bandwidth of the OFDM channel 2. For example, the OFDM management module 55 can change the number of active subcarriers, or the subcarrier spacing, or other parameters.
The base station 50 can notify in advance the OFDM terminal 60 of any change in the operating parameters through corresponding configuration advertisement messages. These messages can be broadcasted on the spread spectrum channel 4 and/or on the OFDM channel 2. However, the advertisements broadcasted on the OFDM channel 2 may not be received by OFDM terminals that are not yet synchronized with the base station 50, whereas the advertisements broadcasted on the static spread spectrum channel 4 may be received by all terminals configured to receive that spread spectrum channel. Therefore, when the terminal 60 is just switched on, it starts to acquire the OFDM physical profile by listening to the spread spectrum channel 4. Once the OFDM management module 65 has received the information to determine the physical profile that is applied, it configures the OFDM baseband module 61, which can then perform the attachment to the base station through the OFDM channel 2. If the terminal 60 is already attached to the base station 50 at the time when a change in physical profile occurs, it can obtain the new profile and the time of change either on the spread spectrum channel 4 or on the OFDM channel 2 (e.g. in a portion of the OFDM frame dedicated to broadcast messages). In an embodiment, the base station uses a broadcast control channel of the OFDM frame for sending an instruction to the terminals 60 located in the corresponding cell, so that the terminals 60 start listening to the spread spectrum channel in response to that instruction. Therefore, the terminals 60 already attached to the base station 50 can obtain the OFDM profile update through the spread spectrum channel 4 without having to be permanently listening to that channel. Alternatively, the operating parameters of the OFDM channel can be broadcasted according to a predefined scheme, e.g. periodically.
In the above embodiment, the OFDM operating parameters are changed for the purpose of spectrum management and dynamic spectrum resource sharing, thereby improving multi-radio co-existence. This embodiment enables a base station to operate several radio standards in the same frequency band while being transparent to legacy systems, e.g. GSM.
The OFDM management module can also serve other purposes than spectrum management, e.g. adapting the OFDM channel to specific requirements of a wireless terminal or to specific transmission conditions. This is illustrated in
Alternatively, the appropriate OFDM physical profile is determined by the OFDM management module 74 of the terminal 70 on the basis of inputs provided by the state monitoring device 73, and then communicated to the base station 80 in the channel adaptation request on the spread spectrum channel.
The physical profile selection and allocation can be implemented with different scopes. For example, the scope can be one terminal, i.e. the selected physical profile is applied to the connection between one terminal and the base station. Alternatively, the scope can be a cell, i.e. the selected physical profile is applied to all connections between terminals located in one cell and the base station. The messages transmitted on the spread spectrum channel include terminal identifiers or connection identifiers, where appropriate, to properly define the scope of the physical profile being negotiated. Besides, the physical profile data may be transmitted in a broadcast mode or in a unicast mode depending on the intended scope.
With an appropriate processing gain, the spread spectrum communication channel, e.g. DSSS, can be made very robust against Doppler shift and multipath reception. Therefore, the spread spectrum channel 4 is very well-suited for communicating with terminals 70 that could be experiencing challenging radio conditions, e.g. moving at a high speed, and for negotiating the physical profile of the OFDM channel. Preferably, the spread spectrum communication modules 72 and 82 are preconfigured for achieving communication in the most difficult foreseen conditions, e.g. at maximum velocity of the terminal.
In an embodiment, the terminal 70 is installed in a land vehicle, such as a high speed train. As a function of the real-time velocity of the vehicle, the OFDM management module 83 selects a set of operating parameter values comprising a sub-carrier spacing value, a number of sub-carrier, an identification of pilot sub-carriers and a cyclic prefix length (i.e. guard time.) An illustrative rule for scaling the sub-carrier spacing is: the higher the velocity, the higher the sub-carrier spacing value. These and other operating parameters can be changed as a function of the physical state of the terminal. Besides, the terminal 70 and the base station 80 can negotiate an OFDM physical profile prior to any synchronization between the OFDM communication modules 71 and 81. This negotiation imposes no prerequisite on the OFDM channel. Therefore, using the spread spectrum channel overlaid in frequency with the OFDM channel, an adaptive modulation scheme in the meaning of Std IEEE 802.16-2004 can be implemented efficiently and further extended to any OFDM operating parameter.
While the above embodiments have been described with reference to OFDM traffic channels, other types of flexible broadband wireless systems can benefit from the same principles for dynamically adapting physical layer parameters, e.g. single-carrier or multi-carrier systems able to operate with variable parameters and configurations, e.g. variable bandwidth.
In another embodiment illustrated by
The operation of the base station and the terminals is similar to the above-described embodiments. Here, spread spectrum communication channel 304 serves to advertise or negotiate the operating parameters of traffic channels having different types, hence different parameters. Preferably, base station 310 communicates the parameters to all terminals using spread spectrum communication channel 305 in broadcast mode.
The traffic channels 301, 302 and 303 are parameterized wireless channels of any type, e.g. OFDM, single-carrier, multi-carrier or other.
Alternatively, the above embodiment with multiple parameterized channels can also be implemented as a point-to-multipoint system or peer-to-peer system comprising multi-standard terminals, i.e. a terminal comprising several traffic communication modules of different types. It will be appreciated that some components can be shared between several communication modules in a multi-standard base station or terminal, e.g. a shared radio front-end.
The functions of the various elements shown in the FIGs., including any functional blocks labeled as “modules”, may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, conventional and/or custom, may also be included.
The invention is not limited to the described embodiments. The appended claims are to be construed as embodying all modification and alternative constructions that may be occurred to one skilled in the art, which fairly fall within the basic teaching here, set forth.
In the claims hereof any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements which performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. Applicant thus regards any means which can provide those functionalities as equivalent as those shown herein.
The use of the verb “to comprise” or “to include” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Furthermore, the use of the article “a” or “an” preceding an element or step does not exclude the presence of a plurality of such elements or steps.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the scope of the claims. Unless otherwise explicitly specified herein, the drawings are not drawn to scale.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07301012.6 | May 2007 | EP | regional |
