Orthogonal Frequency Division Multiplexing (OFDM) is at the heart of current wireless standards and is the main modulation scheme envisioned for use in future generations of wireless communication systems. In this paper we study the performance of precoded OFDM systems in the presence of intentional jamming. Specifically, we consider OFDM systems with sub-band Hadamard precoding for which we derive the expression of the signal-to-jammer+noise-ratio (SJNR) and study how jamming signals with different bandwidths affect the bit error rate (BER) performance of the system.

Game theory has emerged as a new mathematical tool in the analysis and design of wireless communication systems, being particularly useful in studying the interactions among adaptive transmitters that attempt to achieve specific objectives without cooperation. In this paper, we present a game-theoretic approach to the problem of joint transmitter adaptation and power control in wireless systems, where users' transmissions are subject to quality-of-service requirements specified in terms of target signal-to-interference-plus-noise ratios (SINRs) and nonideal vector channels between transmitters and receivers are explicitly considered. Our approach is based on application of separable games, which are a specific class of noncooperative games where the players' cost is a separable function of their strategic choices. We formally state a joint codeword and power adaptation game, which is separable, and we study its properties in terms of its subgames, namely, the codeword adaptation subgame and the power adaptation subgame. We investigate the necessary conditions for an optimal Nash equilibrium and show that this corresponds to an ensemble of user codewords and powers, which maximizes the sum capacity of the corresponding multiaccess vector channel model, and for which the specified target SINRs are achieved with minimum transmitted power.

In this paper, we study the problem of optimizing the pilot-to-data power ratio (PDR) for uplink code-division multiple access (CDMA) systems with partial RAKE (PRAKE) receivers. Both code-division multiplex (CDM) and time-division multiplex (TDM) reference-assisted schemes are considered. We assume Nakagami-m fading channel with two types of power delay profile (PDP): uniform and exponential PDPs. The optimum PDR is derived via minimizing the upper bound of the probability of bit error. A closed-form expression for the optimum PDR is obtained for both CDM and TDM schemes with uniform PDP. For exponential PDP, we derive the condition satisfied by the optimum PDR and obtain it numerically. It is observed that the optimum PDR is noticeably affected by the decay factor, but not by the m-parameter. For exponential PDP, unlike for uniform PDP, the optimum PDR depends on the number of combined paths. We also show that the optimum PDR derived from the block-fading channel model performs favorably in the Jakes' model.

In this paper we present a new algorithm for joint codeword and power adaptation in the uplink of code division multiple access (CDMA) systems, in which codewords are adjusted using gradient-descent interference avoidance, and powers are updated to match target signal-to-interference plus noise-ratio (SINR) values. The proposed algorithm is analyzed and illustrated with numerical examples obtained from simulations.

In this paper we present application of interference avoidance in the context of a general multiple access vector channel model. We show that this monotonically increases sum capacity, and discuss algorithms for code division multiple access (CDMA) codeword optimization based on this procedure. A greedy interference avoidance algorithm for multiaccess vector channels is presented in the paper, for which we discuss convergence to a class of codeword ensembles that satisfy a simultaneous water filling solution and maximize sum capacity. Numerical results obtained from simulations that corroborate our analytical results are also presented.

In this paper we investigate properties of simultaneous water filling for a wireless system with two mutually interfering transmitters and receivers with non-cooperative coding strategies. This is slightly different from the traditional interference channel problem which assumes that transmitters cooperate in their respective coding strategies, and that interference cancellation can be performed at the receivers. In this noncooperative setup, greedy capacity optimization by individual transmitters through various algorithms leads to simultaneous water filling fixed points where the spectrum of the transmit covariance matrix of one user water fills over the spectrum of its corresponding interference-plus-noise covariance matrix, and in our paper we study the properties of these fixed points. We show that at a simultaneous water filling point the eigenvectors of transmit covariance matrices at each receiver are aligned, and identify three regimes which correspond to simultaneous water filling that depend on the interference gains: a) complete spectral overlap, b) partial spectral overlap, and c) spectral segregation. These imply that the transmit covariance matrices will be white in regions of both overlap and segregation, but not necessarily white overall. We also consider performance as a function of interference gain and show that complete spectral overlap is a strongly suboptimal solution over a wide range of gains. Overall, our results suggest that for strong mutual interference, an effort should be made to do joint decoding over receivers since such collaboration can provide large capacity increases. For moderate interference, distributed and/or centralized conflict resolution algorithms would be most effective since more complex collaborative methods do not afford much improvement and strictly greedy methods such as water filling perform poorly, while for weak interference a laissez faire approach seems reasonable

In this paper, we study the problem of optimizing the pilot-to-data power ratio (PDR) for uplink code-division multiple access (CDMA) systems with partial RAKE (PRAKE) receivers. Both code-division multiplex (CDM) and time-division multiplex (TDM) reference-assisted schemes are considered. We assume Nakagami-m fading channel with uniform power delay profile (PDP) and that with exponential PDP. We derive the optinum PDR via minimizing the upper bound of the probability of bit error. For uniform PDP, we present a closed-form expression for the optimum PDR. For exponential PDP, we find the condition satisfied by the optimum PDR and obtain it numerically. For exponential PDP, unlike for uniform PDP, the optimum PDR depends on the number of combined paths. However, the effect of the number of combined paths on the optimum PDR is not significant.

We consider a communication system with multiple independent user-base pairings in a white Gaussian noise environment, and for which a simultaneous water filling condition is satisfied by users at their respective bases. We focus on the weak mutual interference case for which the simultaneous water filling solution is unique and corresponds to complete user overlap in signal space. We show that when users at other bases are treated as Gaussian noise, simple separation of users in signal space usually offers better performance than simultaneous water filling, and present a distributed algorithm which separates users in signal space.

We consider a wireless system with base stations which collaborate, and derive bounds on sum capacity and total squared correlation for uniform channels between users and bases. The correspondence also investigates structural properties which must be satisfied by user transmit covariance matrices at the optimal sum capacity/total squared correlation (TSC) point, and shows that for multibase systems, maximizing sum capacity and minimizing TSC are, in general, not equivalent problems.

Consider a wireless system with multiple and independent user-base pairings over some region. Each user tries to greedily optimize its performance, and eventually a simultaneous water-filling fixed point is reached. Here we seek to analytically understand properties of different water-filling fixed points. In so doing we show that water-filling alone does not generally result in optimum resource sharing and in some cases is a poor solution. We close by suggesting dynamic strategies for performance enhancement.