This paper presents an overview of progress in the area of multiple input multiple output (MIMO) space-time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of techniques and algorithms proposed which attempt to realize the various benefits of MIMO including spatial multiplexing and space-time coding schemes. These algorithms are often derived and analyzed under ideal independent fading conditions. We present the state of the art in channel modeling and measurements, leading to a better understanding of actual MIMO gains. Finally, the paper addresses current questions regarding the integration of MIMO links in practical wireless systems and standards.

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From theory to practice: an overview of MIMO space-time coded wireless systems

A multiple-access MIMO WLAN system that employs MIMO, OFDM, and TDD. The system (1) uses a channel structure with a number of configurable transport channels, (2) supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities, (3) employs a pilot structure with several types of pilot (e.g., beacon, MIMO, steered reference, and carrier pilots) for different functions, (4) implements rate, timing, and power control loops for proper system operation, and (5) employs random access for system access by the user terminals, fast acknowledgment, and quick resource assignments. Calibration may be performed to account for differences in the frequency responses of transmit/receive chains at the access point and user terminals. The spatial processing may then be simplified by taking advantage of the reciprocal nature of the downlink and uplink and the calibration.

MIMO WLAN system

Link adaptation techniques, where the modulation, coding rate, and/or other signal transmission parameters are dynamically adapted to the changing channel conditions, have emerged as powerful tools for increasing the data rate and spectral efficiency of wireless data-centric networks. While there has been significant progress on understanding the theoretical aspects of time adaptation in LA protocols, new challenges surface when dynamic transmission techniques are employed in broadband wireless networks with multiple signaling dimensions. Those additional dimensions are mainly frequency, especially in multicarrier systems, and space in multiple-antenna systems, particularly multiarray multiple-input multiple-output communication systems. We give an overview of the challenges and promises of link adaptation in future broadband wireless networks. We suggest guidelines to help in the design of robust, complexity/cost-effective algorithms for these future wireless networks.

Adaptive modulation and MIMO coding for broadband wireless data networks

Techniques to schedule terminals for data transmission on the downlink and/or uplink in a MIMO-OFDM system based on the spatial and/or frequency “signatures” of the terminals. A scheduler forms one or more sets of terminals for possible (downlink or uplink) data transmission for each of a number of frequency bands. One or more sub-hypotheses may further be formed for each hypothesis, with each sub-hypothesis corresponding to (1) specific assignments of transmit antennas to the terminal(s) in the hypothesis (for the downlink) or (2) a specific order for processing the uplink data transmissions from the terminal(s) (for the uplink). The performance of each sub-hypothesis is then evaluated (e.g., based on one or more performance metrics). One sub-hypothesis is then selected for each frequency band based on the evaluated performance, and the one or more terminals in each selected sub-hypothesis are then scheduled for data transmission on the corresponding frequency band.

Resource allocation for MIMO-OFDM communication systems

A method and apparatus for allocating subcarriers in an orthogonal frequency division multiple access (OFDMA) system is described. In one embodiment, the method comprises allocating at least one diversity cluster of subcarriers to a first subscriber and allocating at least one coherence cluster to a second subscriber.

Ofdma with adaptive subcarrier-cluster configuration and selective loading

Embodiments of a system and method of classifying remote users according to link quality, and scheduling wireless transmission of information to the users based upon the classifications are generally disclosed

System and method of classifying remote users according to link quality, and scheduling wireless transmission of information to the to the users based upon the classifications

A technique for rapidly and efficiently adjusting characteristics of communication in a time-and-frequency varying channel involves the adaptive selection of a transmission mode (i.e., various kinds of modulation, coding, and antenna combining schemes) and a channelization mode (i.e., the manner in which the spectrum is used during transmission). The method includes determining signal quality estimates [32] from received signals, deriving a set of transmission mode parameters [38] from the estimates, and sending parameters [38] as feedback [40] from a receiver to a transmitter. In one embodiment, each of the transmission mode parameters [38] is a transmission mode selected for use with one of the system channelization modes. In another embodiment, transmission mode parameters [38] comprise one parameter selected for use with any system channelization mode. The method also comprises deriving a set of channelization mode parameters from channel traffic workload information and possibly other information. A single channelization mode [48] is selected from the set of channelization mode parameters, and a single transmission mode [50] is selected from the set of transmission mode parameters. The transmission mode and channelization mode may be selected jointly; or the channelization mode may be selected independently, after which the corresponding transmission mode is selected in dependence upon the selected channelization mode. In the case where only one transmission mode parameter is sent as feedback, the transmission mode selection is trivial and independent of the selected channelization mode. The selected transmission mode and channelization mode are then used for encoding and modulation [54] prior to transmission of information over the communication channel.

Wireless communication systems with adaptive channelization and link adaptation

This article presents emerging technologies for upcoming non-line-of-sight fixed or stationary broadband wireless access systems. We describe design trade-offs for overall maximization of the radio capacity and coverage of fixed wireless access (FWA) in multicell interference- and fading-prone environments. We characterize quantitatively the impact of key emerging radio technologies on the overall performance.

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Technologies and performance for non-line-of-sight broadband wireless access networks

A communications receiver may include an adaptive filter unit for removing coherent interference components from a received signal. In the absence of a signal of interest, the filter may adapt dynamically to remove current interference components. When a signal of interest is detected, the filter may be controlled to stop (or at least reduce) its adaptation, to prevent removal of the signal of interest. The received signal may be down-converted to a complex baseband by conditioning circuitry. A detector may detect the signal of interest, and control the filter. Autocorrelation may be used to estimate a characteristic of the signal of interest in the complex baseband. The detector may include hysteresis to react quickly to the start of signal of interest, and more slowly to an end of the signal of interest. The signal of interest may be a frequency shift keyed (FSK) signal. A demodulator may demodulate FSK components based on the autocorrelation result. The characteristic of the signal of interest used for detection and/or demodulation may be a directional characteristic of a vector representing the complex baseband signal in complex space.

Suppressing interference for wireless reception and improvements relating to processing a frequency shift keyed signal

A circuit and method for suppressing interference components in a received signal are provided. The circuit includes an adaptive filter configured to process a first quantity of digital signal samples per unit time when the adaptive filter is operating in a first mode, and a second quantity of digital signal samples per unit time when operating in a second mode, wherein the first quantity is less than the second quantity. The method includes implementing an adaptive filter configured to operate in an adaptive mode and in a second mode having a reduced adaptability compared to the adaptive mode; operating the adaptive filter in the adaptive mode to process a first quantity of digital signal samples per unit time; and operating the adaptive filter in the second mode to process a second quantity of digital signal samples per unit time; wherein the first quantity is less than the second quantity.

Luc Haumonte

Papers

System and method of classifying remote users according to link quality, and scheduling wireless transmission of information to the to the users based upon the classifications

Wireless communication systems with adaptive channelization and link adaptation

Technologies and performance for non-line-of-sight broadband wireless access networks

Suppressing interference for wireless reception and improvements relating to processing a frequency shift keyed signal

Circuit and method for suppressing interference components in received signal