A. C. McCormick

A comparison of convolutional and Walsh coding in OFDM wireless LAN systems

A Walsh coded OFDM system is described which could provide an alternative to convolutional coding in packet based wireless LAN systems. This allows lower complexity decoding and lower peak-to-average power ratios. This system is compared with a hard decision decoded convolutional receiver, based on the OFDM specifications for the IEEE 802.11 and ETSI HIPERLAN/2 physical layer standards. In multipath environments, the high diversity Walsh coded OFDM system shows large improvements over uncoded systems and similar performance to the more computationally complex convolutional receivers.

A differential phase-shift keying multicarrier code division multiple access system with an equal gain combining receiver

Multicarrier code division multiple access (MC-CDMA) is a spread-spectrum technique which allows simple implementation of multiuser detection techniques. Combining this with differential phase-shift keying (DPSK) allows a low complexity receiver design which achieves the channel estimation implicitly. If only downlink communication is considered, performing the DPSK at a subcarrier level allows significant performance gains and employing a joint phase estimation approach for all users signals allows the implementation of an effective equal gain combining receiver. Theoretical predictions and simulations of the performance in additive white Gaussian noise are demonstrated. Comparison with similar systems is shown through simulations in a fast fading typical mobile channel.

A carrier frequency offset correction scheme for MC-CDMA

A novel algorithm for carrier frequency offset correction in MC-CDMA is investigated. The algorithm uses coherently detected data symbols to provide phase offset information, which is used to modify the carrier frequency and successively reduce the offset with every data symbol. Comparison between this frequency correction algorithm, a closely related phase compensation algorithm and a two-symbol maximum likelihood estimation algorithm is provided.

A novel interference cancellation receiver for uplink multi-carrier CDMA

A novel receiver for uplink multi-carrier CDMA, which combines elements of parallel, successive and maximum likelihood detection is described. The performance of this receiver is compared with other similar detectors using simulations with a Rayleigh fading channel model. A reduction in computation time and complexity over the decision statistic ordered successive interference cancellation algorithm is shown with marginal loss in performance.

A low power MMSE receiver architecture for multi-carrier CDMA

The power consumption of a minimum mean square error (MMSE) multi-carrier CDMA (code division multiple access) receiver implemented in digital hardware is considered. A new low power block based architecture is implemented for the combiner subsystem, and compared with a multiply accumulate circuit approach. Simulations using data consistent with typical performance of a multi-carrier CDMA receiver indicate that the block based approach can produce a power reduction of around 50%.

Implementation of a sic based MC‐CDMA base station receiver

Investigation of the performance of uplink multi-carrier code-division multiple access (MC-CDMA) receiver designs [1] has indicated that the inclusion of decision statistic ordered successive interference cancellation (SIC) [2] in the receiver provides good performance for a large number of users with an algorithm of only complexity. Accurate channel estimation can be a problem in uplink MC-CDMA, but if the channels have a small delay spread, narrowband pilots and interpolation can be applied to provide accurate channel estimates, without requiring a high pilot signal to noise ratio. The hardware implementation of low power MC-CDMA mobile stations has been considered in [3]. This work is extended to the uplink in this paper. In particular the implementation of the decision statistic ordered SIC algorithm is considered. Although much of the SIC algorithm requires serial operation, some parallelisation can be applied to reduce the number of clock cycles required from to . A 48 user QPSK system is considered and therefore a reduction of clock rate from times the symbol rate to times the symbol rate is desirable, however both serial and parallel architectures will be investigated.

Walsh coding across multiple antennas for high data rate wireless services

The combination of Walsh coding with a layered space-time architecture is investigated. This provides a system with flexible coding rates and low complexity linear decoding. The codes allow exploitation of the diversity of the multiple antenna channel while allowing code rates up to 1, while still providing a performance improvement over an uncoded system. Simulations provide comparison with repetition coded and uncoded systems.

Wideband and Narrowband Interference Cancellation for Asynchronous MC-CDMA

Uplink MC-CDMA is asynchronous, and each user’s signal experiences independent fading, therefore the low complexity, linear narrowband receivers used for downlink are not applicable. However, in this case, wideband interference cancellation schemes can provide good multi-user detection. If the asynchron ism is constrained to a fraction of the symbol length, a narrowband interference cancellation scheme can be applied. This approach has lower complexity than wideband cancellation, although there may be some degradation in performance. This degradation is estimated for both successive and parallel interference cancellation algorithms, through simulations of their performance in AWGN and indoor wireless channels.