Performance Analysis Of Anti-jamming For Coherent Fast Frequency Hopping Systems

Frequency Hopping Spreading Spectrum (FHSS) is a kind of well-known and widely used spread spectrum system, it has attracted great interest for combating intentional and unintentional jamming. Traditionally the noncoherent frequency-shift-keying (FSK) is more commonly used in FHSS systems due to its simplicity compared with the coherent phase-shift-keying (PSK) scheme. However, noncoherent systems suffer significant performance degradation due to the noncoherent demodulation and diversity combining loss. To fully recover the noncoherent demodulation and diversity combining loss, researchers have studied a solution which is to maintain a continuous phase at the transmitter from one hop to another to make coherent reception feasible and proposed a frequency diversity scheme for the phase-coherent FHSS system.However, it appears from the literature that the performance analysis of a coherent FHSS system in only limited to the slow frequency hopping (SFH) system, the research on the fast frequency hopping (FFH) system is not enough comprehensive and in-depth. The paper extends the performance analysis of a coherent FHSS from SFH to FFH, examine the bit-error-rate (BER) performance separately of a coherent FFH system employing BPSK with diversity countering partial-band noise jamming (PBNJ), multi-tone noise jamming (MTNJ) and follower/repeater noise jamming (FRNJ) in the presence of additive white Gaussian noise (AWGN) with three types of coherent receivers, namely, the maximum-likelihood (ML) receiver, the linear-combination (LC) receiver, and the hard-decision majority-vote (HDMV) receiver, the BER expressions for such receivers are derived and validated by simulation results. It shows that the coherent ML receiver gives the best performance, followed by the coherent HDMV receiver and the coherent LC receiver. The coherent ML receiver can counter PBNJ, MTNJ and FRNJ effectively, and the BER performance of system improves as the diversity level increases, although the incremental improvement will diminish eventually when the diversity level is sufficiently large. The coherent LC receiver is incapable of providing diversity improvement but the coherent HDMV receiver has an optimum diversity level for a specific signal-to-jamming ratio (SJR) and signal-to-noise ratio (SNR) under the worst-case PBNJ, worst-case MTNJ and FRNJ.