Physical and MAC Layer Cognition using Multi-mode Multi-rate Waveform for SDR based Ad-hoc Networks

Abstract

Modern-day technology has set very high standards for robust, reliable, and high-speed communications. Software defined radios (SDR) have provided the platform to researchers in designing ad-hoc networks addressing these standards. SDR networks are required to achieve endurance, reliability, efficient data transmission, portability, and adaptability to various operating requirements. Their immediate deployment in perilous ventures without the use of any permanent infrastructure has made them an inevitable choice for ad-hoc tactical scenarios. Increasing demands of adaptability and reconfigurability impose many challenges on the design of SDR waveforms even for highly heterogeneous wireless networks. Narrowband waveforms provide robustness and work for longer distances but lack in providing higher throughput, whereas, wideband waveforms provide much higher data rates at the cost of reduced robustness and shorter ranges. A heterogeneous SDR network having diverse quality of service (QoS), range requirements, and channel conditions cannot fully rely on one of the narrowband or wideband waveforms. This piece of work proposes a multi-mode multi-rate physical layer with a hybrid narrowband/wideband (NBWB) networking waveform. The concept is based on simultaneous transmission and reception of signals having multiple bandwidths through the analog wideband front end. A digital front-end architecture is presented which uses the sample rate conversion and channelization of multiple signals. This formulates a composite signal which is then transmitted by using the configuration of wideband RF front end. At the receiver, the composite signal is received by using the same front end configured in wideband mode. Apart from physical layer concerns of range and robustness addressed by the physical layer, significant efforts have been made in the past in cross-layer design to achieve maximal efficiency and higher throughput. In this research, a cross-layer solution is proposed which consists of medium access control (MAC) layer design providing an intelligent channel allocation scheme supported by the presented multi-mode multi-rate physical layer. This research also proposes a cognitive engine that further empowers this cross-layer design approach to achieve high data rates, improved quality of service (QoS), and adaptive range capabilities. The presented physical layer exhibits a mixed-use of narrowband and wideband waveforms. The cross-layer design proposes a reduction in both control and data phase latency. MAC layer ensures the maximal utilization of the time and frequency spectrum. Bandwidth and delay optimizations are also managed by the proposed trio of the physical layer, MAC, and cognition to reduce latency and achieve desired QoS.