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

A MIMO system supports multiple spatial multiplexing modes for improved performance and greater flexibility. These modes may include (1) a single-user steered mode that transmits multiple data streams on orthogonal spatial channels to a single receiver, (2) a single-user non-steered mode that transmits multiple data streams from multiple antennas to a single receiver without spatial processing at a transmitter, (3) a multi-user steered mode that transmits multiple data streams simultaneously to multiple receivers with spatial processing at a transmitter, and (4) a multi-user non-steered mode that transmits multiple data streams from multiple antennas (co-located or non co-located) without spatial processing at the transmitter(s) to receiver(s) having multiple antennas. For each set of user terminal(s) selected for data transmission on the downlink and/or uplink, a spatial multiplexing mode is selected for the user terminal set from among the multiple spatial multiplexing modes supported by the system.

MIMO system with multiple spatial multiplexing modes

Pilots suitable for use in MIMO systems and capable of supporting various functions are described. The various types of pilot include - a beacon pilot, a MIMO pilot, a steered reference or steered pilot, and a carrier pilot. The beacon pilot is transmitted from all transmit antennas and may be used for timing and frequency acquisition. The MIMO pilot is transmitted from all transmit antennas but is covered with different orthogonal codes assigned to the transmit antennas. The MIMO pilot may be used for channel estimation. The steered reference is transmitted on specific eigenmodes of a MIMO channel and is user terminal specific. The steered reference may be used for channel estimation. The carrier pilot may be transmitted on designated subbands/antennas and may be used for phase tracking of a carrier signal. Various pilot transmission schemes may be devised based on different combinations of these various types of pilot.

Pilots for mimo communication systems

For transmit diversity in a multi-antenna OFDM system, a transmitter encodes, interleaves, and symbol maps traffic data to obtain data symbols. The transmitter processes each pair of data symbols to obtain two pairs of transmit symbols for transmission from a pair of antennas either (1) in two OFDM symbol periods for space-time transmit diversity or (2) on two subbands for space-frequency transmit diversity. N T ·(N T −1)/2 different antenna pairs are used for data transmission, with different antenna pairs being used for adjacent subbands, where N T is the number of antennas. The system may support multiple OFDM symbol sizes. The same coding, interleaving, and modulation schemes are used for different OFDM symbol sizes to simplify the transmitter and receiver processing. The transmitter performs OFDM modulation on the transmit symbol stream for each antenna in accordance with the selected OFDM symbol size. The receiver performs the complementary processing.

Transmit diversity processing for a multi-antenna communication system

System traffic may be arranged into different categories (e.g., control data, user data, and pilot data). For each category, one or more OFDM symbols of the proper sizes may be selected for use based on the expected payload size for the traffic in that category. For example, control data may be transmitted using OFDM symbols of a first size, user data may be transmitted using OFDM symbols of the first size and a second size, and pilot data may be transmitted using OFDM symbols of a third size or the first size. In one exemplary design, a small OFDM symbol is utilized for pilot and for transport channels used to send control data, and a large OFDM symbol and the small OFDM symbol are utilized for transport channels used to send user data.

Ofdm communication system with multiple ofdm symbol sizes

A communication device includes a noise flattening filter having a filter response that dynamically adjusts based on the current noise spectrum in a wireless channel. The noise spectrum of the wireless channel is estimated and used to determine a noise classification for the channel. A noise flattening filter response is then selected based upon the noise classification for use in filtering signals received from the channel. The filtered signals are then delivered to an equalizer for further processing.

Noise dependent filter

A receiver includes a searcher to identify pilot signals within a received signal and a pilot tracking unit to continuously track pilot signals identified by the searcher. The pilot signals tracked by the pilot tracking unit may include pilot signals associated with an affiliated base station as well as pilot signals associated with non-affiliated base stations. In at least one embodiment, the pilot tracking unit continuously tracks most or all of the pilot signals identified by the searcher.

Novel receiver architecture for cdma receiver downlink

A receiver in a wireless communication system utilizes a metric to minimize the error probability in transmitted information. The receiver may use a detector utilizing multiuser detection or rake detection. The output symbols of the detector are examined and a metric is obtained related to the noise and interference that may have distorted the transmission of the symbol. This metric is supplied to a channel decoder along with the symbol to improve decoding.

Metric correction for multi user detection, for long codes DS-CDMA

A multi-user detector for use in a CDMA receiver system includes a channel tap interpolator to generate interpolated channel taps for users of interest. The interpolated channel taps occur at integer multiples of a chip period from a sampling reference point. The channel tap interpolation allows detection processing to proceed in the chip domain, rather than in the sample domain, thus reducing the complexity of the multi-user solution significantly. In at least one approach, a number of low dimensionality “virtual” users are defined based on the recursive property of the spreading sequences. Solutions may then be developed for the virtual users using conventional detection (e.g., MMSE) techniques.

Low complexity multiuser detector

This paper considers the link-level and network-level performance of code division multiple access (CDMA) pilot interference cancellation (pilot IC) technology, a low-complexity advanced receiver technology being considered for use in commercial third generation (3G) CDMA cellular systems. The concept behind this technology is to estimate and cancel at the handset receiver the interference effects associated with CDMA downlink pilot signals broadcast from the base stations of the network. The canceling of interference at the receiver improves the signal-to-interference/noise ratio (SINR), which enables increased cell capacity or throughput. In this paper, we derive SINR expressions for evaluating the probability of error performance of both the RAKE and pilot IC handset receivers, under conventional random spreading code assumptions. The approach can easily and accurately model a wide variety of transmitter, channel, and receiver conditions, including the effects of channel estimation. We also utilize radio network simulations to illustrate and quantify the capacity gains available for 3G CDMA networks through the use of pilot IC handsets. Network simulations are also used to examine the reduced level of soft-handoff found to be possible in pilot IC-based networks and the increased flexibility available in setting pilot power levels. We further consider the impact of using stronger pilot signals for improving the demodulation performance of sensitive higher-order modulation constellations that are needed to support spectrally efficient high-rate data services.

Yoni Perets

Papers

Noise dependent filter

Novel receiver architecture for cdma receiver downlink

Metric correction for multi user detection, for long codes DS-CDMA

Low complexity multiuser detector

Pilot interference cancellation technology for CDMA cellular networks