Interference avoidance and multiuser MIMO systems

Abstract

SUMMARYWe apply interference avoidance methods to multiuser systems with multiple inputs and multiple outputs (MIMO) such as would be used on the uplink (or in overlapping downlink footprints) for satellite systems with multiple antennas. An arbitrary signal space can be used and the method can be applied to any MIMO system model regardless of the choice signal basis functions. Information is transmitted via multicode CDMA where symbols that comprise the data frame from a given user are 'spread' over the available dimensions using a precoding matrix. Optimal precoding matrices that maximize signal-tointerference plus noise-ratio for all symbols/users are then obtained by application of distributed greedy interference avoidance methods. In general, algorithms based on greedy interference avoidance are different from water filling schemes. However, the codeword ensembles obtained provide similar simultaneous water filling solutions and thus maximize sum capacity. Numerical simulations have been performed and the signal-to-noise ratio distribution for receiver antennas and complementary cumulative distribution functions for sum capacity with optimal precoding matrices are also presented.

Greedy SINR Maximization in Collaborative Multibase Wireless Systems

“…If we assume that the noise is stationary with fixed covariance matrix W, then (8) shows that maximizing the sum capacity is equivalent to maximizing |R|. According to [20], this implies that a water filling condition is satisfied for all users simultaneously, for which eigenvectors of the interferenceplus-noise covariance matrix seen by a given user align with those of its transmit covariance matrix X whose eigenvalues satisfy the well-known water-filling condition [13, page 253].…”

“…We note that the sum capacity expression in (8) has been used in the context of previous works on multiuser MIMO systems [19,23,24]. Our objective is to define a codeword adaptation algorithm for the system described by (4) which iteratively updates codewords of all users until an optimal ensemble of codewords is obtained.…”

“…We also note that the proposed SINR maximization algorithm is a greedy interference avoidance algorithm [11] since at each step, it greedily maximizes the SINR of an individual codeword without paying attention to the consequences that this action may have on the ensemble of codewords. Different interference avoidance algorithms have been previously derived for general multiaccess vector channels [26] as well as for multiuser MIMO systems [8].…”

“…In particular, the problem of optimizing CDMA codewords has been addressed by several researchers which have established algorithms that yield optimal codeword ensembles for CDMA systems [1,2,3,4,5,6]. Recently, optimal codeword ensembles for CDMA systems have also been obtained by application of interference avoidance methods [7,8,9,10,11,12] which provide distributed algorithms for codeword optimization in CDMA systems by which users independently adjust codewords in response to changing patterns of interference.…”

Interference avoidance for wireless systems

“…A similar signal space approach is used to apply the generalized eigen-algorithm for codeword optimization in very general asynchronous CDMA system models [16,32]. We note that for particular cases less general interference avoidance algorithms can be used [33].…”