On cross-layer interaction for link adaptation in MIMO-enabled wireless networks

Abstract

The standard solution to the problem of radio link instability is called link adaptation (LA), and is applied in many existing wireless networks. LA is the process of adjusting the wireless link parameters, following the changes of the radio channel conditions so that an optimal link quality is achieved. The controlled link parameters vary from system to system. In addition, the idea behind cross-layer interaction (CLI) is to integrate the resources and information available in the different fractures and to create a system that can be highly adaptive by sharing state information between different processes or modules in the system. Particularly, in this thesis, we are interested in interactions between the physical (PHY) and medium access control (MAC) layers through theoretical link quality acquisition (LQA) for wireless channels. Accordingly, this thesis proposes LA technologies using theoretical LQA and investigates their performance in various multiple-input multiple-output (MIMO) based networks in order to maximize the system throughput in tandem with stabilizing the link condition.

First of all, we introduce a new LA approach called the adaptive modulation, coding, and spatial mode (AMCS) scheme for MIMO bit-interleaved coded orthogonal frequency division multiplexing (MIMO BIC-OFDM) systems. The AMCS technique can provide both minimal performance degradation and significant throughput gain by controlling the spatial streams. With this technique, we can derive a simple and accurate closed-form expression of an instantaneous bit error rate (I-BER). Based on the I-BER, the proposed AMCS scheme chooses an appropriate modulation, coding, and spatial mode (MCS) type that improves the system performance while satisfying the quality of service (QoS) requirement. A simplified MCS type search method is also proposed, which allows the receiver to effectively select a MCS type and then send it back to the transmitter by using only a small amount of information bi...