In this paper, we study the performance of base station (BS) cooperation for downlink transmission. Based on a modified Wyner multicell model, an opportunistic intra cell scheduling scheme is proposed. Then, we derive a closed-form expression for the sum-rate capacity of the proposed scheme in the Rayleigh flat-fading channel. Also, we prove that the opportunistic scheme can be regarded as providing a downlink beam-forming scheme to achieve a tighter lower bound for the downlink sum rate capacity. Numerical results confirm our theoretical analysis.

This paper studies the optimum combining (OC) system with multiple arbitrary-power interferers and thermal noise in a flat Rayleigh fading environment. The main contribution of the paper is a concise performance analysis for the overload OC system where the number of interferers exceeds or is equal to the number of antennas elements. Simple closed-form formulas are derived for the moment generating function (m.g.f) of the output signal-to-interference-plus-noise ratio (SINR) and the symbol error rate (SER) with M-ary phase shift keying (M-PSK). These formulas are expressed as a finite sum involving polynomial, exponential and exponential integral terms. Based on the derived m.g.f, the closed-form explicit expressions for the moments of the output SINR are determined. Finally, asymptotic analysis illustrates that employing distinguished power control is an effective approach to combat the SER floor for the overload OC system.

This letter studies secure transmission design with finite alphabet input for cooperative jamming network under individual power constraint. By adopting the zero-force scheme, where the jamming signal is fully laid in the null space of the relay-destination channel, the problem of enhancing the achievable secrecy rate is decomposed into two independent subproblems: relay weights design and power control. We reveal that the problem of relay weights design is identical to the problem of minimizing the maximal equivalent source-eavesdropper channel gain, which can be transformed into a semi-definite programming (SDP) problem and thus is tackled using interior point method. Besides, the problem of power control is solved with the fundamental relation between mutual information and minimum mean square error (MMSE). Numerical results show that the proposed scheme achieves significant performance gains compared to the conventional Gaussian design.