Performance enhancement of frequency hopping systems in the presence of interference

In Chapter 1, the basic philosophy of frequency hopping is introduced and two main types of FH systems, namely slow frequency hopping (SFH) and fast frequency hopping (FFH) are discussed. Furthermore, a comparative study of various diversity combining techniques used in FFH assisted MFSK systems is presented, when the system is exposed to partial band noise jamming (PBNJ) and multitone jamming (MTJ). In Chapter 2, the performance of Reed Solomon (RS) coded SFH-MFSK systems using various low-complexity erasure insertion (EI) schemes is investigated, when communicating over Rayleigh fading channels in the presence of MTJ. Three different EI schemes are considered, which are based on the output threshold test (OTT), on the ratio threshold test (RTT) and on the joint maximum output-ratio threshold test (MO-RTT). The relevant statistics of these EI schemes are investigated mathematically and based on these statistics, the performance of the EI schemes is evaluated in the context of error-and-erasure RS decoding and compared to the performance of error-correction only decoding. In Chapter 3, a novel method of bit error ratio (BER) analysis of product combining (PC) used in FFH-MFSK has been proposed. This method employs Mellin transform which is a convenient tool for determining the probability density function of a product of random variables. The relevant decision statistics have been derived in semi-closed form when the system operates in a Rayleigh fading channel contaminated by PBNJ. Derivation of these statistics facilitates computation of the system’s BER. This method facilitates for the first time the analysis of the FFH PC receiver using modulation orders higher than 2. In Chapter 4, the FFH-MFSK system is considered in a land mobile communication system, where a base station (BS) supports multiple users. The ability of a range of diversity combining schemes to combat multi-user interference is evaluated. Furthermore, two successive interference cancellation techniques have been proposed for multi-user detection at the BS receiver. These techniques employ various reliability tests to carryout symbol detection in multiple stages. Our simulation results show that an attractive BER performance can be achieved when these techniques are employed in a FFH-MFSK system operating in multiple access scenarios. In Chapter 5, iterative decoding designed for FFH-MFSK is investigated. The soft information generated by the FFH demodulator and passed to the outer decoder is derived for various channel models. The convergence behaviour of the iterative scheme is investigated employing Extrinsic Information Transfer (EXIT) charts, casting light on the various parameters that influence its interactive gain. Furthermore, a novel interference cancellation scheme that operates in conjunction with a soft-input-soft-output decoder is proposed. Our simulation results demonstrate that this scheme significantly enhances the multiple access capability of the FFH system.