Joint adaptive modulation and adaptive MIMO system for fading channels in 3GPP LTE

This paper presents joint adaptive modulation and multiple-input multiple-output (MIMO) system (JAMAMS) in Long Term Evolution (LTE) network that adapts both modulation type and MIMO scheme based on channel conditions. Specifically, four adaptive modulation-based MIMO techniques, namely, 1 × 2 MIMO with maximum ratio combining (MRC); 2 × 1 and 2 × 2 Alamouti techniques; and 2 × 2 Vertical Bell Labs Layered Space-Time Architecture (V-BLAST) are investigated. Bit error rate (BER) and spectral efficiency (SE) are used as performance metrics and Zero Forcing (ZF) detection is used in all the MIMO techniques. For each of the four techniques, first the signal-to-noise (SNR) thresholds for switching from one modulation order to the next (i.e., adaptive modulation) are determined. Then, based on comparison of the thresholds of the four schemes, a proposal is made when the system has to switch from one MIMO scheme to the other; and the resulting system is called JAMAMS. In the uplink scenario, as an example, adaptive modulation-based 2 × 2 Alamouti, 1 × 2 scheme with MRC, and 2 × 2 V-BLAST schemes have shown “optimal” SE performance in the SNR ranges 4-19 dB, 19 dB-28 dB, and greater than 28 dB, respectively, while satisfying target BER constraint, BER_th ≤ 10^-2. Moreover, it is shown that JAMAMS has comparable computational complexity in comparison to fixed MIMO systems.