In this paper we describe a coding, modulation, and spatial processing technique for fixed broadband wireless Internet access applications and provide examples of its performance. This technique is built on orthogonal frequency division multiplexing (OFDM) and is known as vector OFDM (VOFDM). We compare VOFDM with conventional single carrier modulation (SCM), and show that it provides substantial performance improvements over SCM.

This paper explores the improvement in information capacity and practical data rate that is possible with adaptive antenna technology applied to wireless-multipath communication channels. Whereas the conventional view is that multipath-signal propagation is an impediment to reliable communication, this paper shows that multipath can actually multiply the achievable data rate for wireless channels provided that the appropriate communication structure is employed. Multivariate discrete multitone (MDMT) combined with multivariate trellis-coded modulation (MTCM) is proposed and analyzed as a practical means of realizing a multiplicative-rate advantage in the case where channel-state information is not available at the transmitter. In Rayleigh fading, these new techniques are shown to simultaneously achieve a multiplicative data-rate advantage and lower error rate as compared to conventional coded orthogonal-frequency division multiplexing. Optimal minimum mean square error (MMSE), adaptive MDMT channel-estimation techniques are derived. The effects of channel-estimation error on MTCM are analyzed.

Multipath signal propagation has long been viewed as an impairment to reliable communication in wireless channels. This paper shows that the presence of multipath greatly improves achievable data rate if the appropriate communication structure is employed. A compact model is developed for the multiple-input multiple-output (MIMO) dispersive spatially selective wireless communication channel. The multivariate information capacity is analyzed. For high signal-to-noise ratio (SNR) conditions, the MIMO channel can exhibit a capacity slope in bits per decibel of power increase that is proportional to the minimum of the number multipath components, the number of input antennas, or the number of output antennas. This desirable result is contrasted with the lower capacity slope of the well-studied case with multiple antennas at only one side of the radio link. A spatio-temporal vector-coding (STVC) communication structure is suggested as a means for achieving MIMO channel capacity. The complexity of STVC motivates a more practical reduced-complexity discrete matrix multitone (DMMT) space-frequency coding approach. Both of these structures are shown to be asymptotically optimum. An adaptive-lattice trellis-coding technique is suggested as a method for coding across the space and frequency dimensions that exist in the DMMT channel. Experimental examples that support the theoretical results are presented.

Methods are reported for adaptive phased array transmission of digital wireless communication signals for the purpose of improving network call capacity. Frequency division duplex (FDD), time division multiple access (TDMA) communication channels are considered. The proposed techniques are designed for severe multipath environments with large Doppler, angle and delay spreads. No knowledge of array geometry, propagation path angles or portable feedback is required to adapt the transmission weight vectors. The time or frequency averaged spatial covariance of the received reverse link signal vector is decomposed into desired signal and interference subspaces which are used to form quadratic optimization problems involving matched filter bound cost functions. A dynamic channel allocation algorithm searches for frequency channels in which the adjacent cell portables are spatially compatible with the desired portable. Results of cellular network simulations are provided to illustrate the network call capacity improvements that are possible with the proposed FDD transmission approach.

A simple adaptive technique is proposed for separation and demodulation of multiple co-channel frequency modulated (FM) signals received at an antenna array. The proposed method, which for FM signals is embodied in an architecture referred to as a multitarget adaptive phase-lock loop (MADPLL), exploits known signal structure through a complete demodulation and remodulation of the signals. The two properties of the signal that are exploited here are the known bandwidth of the information signal and the constant-modulus (CM) property of FM signals. It is shown that the proposed method can lead to significant improvements in performance over methods that exploit only the CM property.