Barry K. Levitt

FH/MFSK Performance in Multitone Jamming

The performance of frequency-hopped (FH) M -ary frequency-shift keyed (MFSK) signals in partial-band noise has been extensively analyzed in the open literature. This paper extends the previous research to the usually more effective class of multitone jamming. Specifically, this paper will 1) categorize several different multitone jamming strategies; 2) analyze the performance of FH/MFSK signaling, both uncoded and with diversity, assuming a noncoherent energy-detection metric with linear combining and perfect jamming-state side information, in the presence of worst-case interference for each of these multitone categories; 3) compare the effectiveness of the various multitone jamming techniques, and contrast the results with the partial-band noise jamming case.

Use of Diversity to Improve FH/MFSK Performance in Worst Case Partial Band Noise and Multitone Jamming

The performance of an uncoded frequency-hopped (FH), M-ary frequency-shift keyed (MFSK) communication system can be severely degraded by worst case partial band noise or multitone jamming. This paper demonstrates that time diversity, a simplified form of coding, will effectively recover most of this jamming loss, particularly at low error rates.

Optimum detection of slow frequency-hopped signals

Optimum detectors have previously been derived for fast frequency-hopped (FFH) signals with M-ary frequency-shift-keyed (MFSK) data modulation received in additive white Gaussian noise (FFH here implies that a single MFSK tone is transmitted per hop), The present paper extends that work to the more analytically complex category of slow frequency-hopped (SFH) signals with multiple MFSK tones per hop. A special subset of the SFH/MFSK format that receives particular attention in the paper is the case of continuous-phase modulation (CPM) for which the carrier phase is assumed to be constant over the entire hop. A fundamental conclusion is that SFW/CPM modulation is advantageous not only to the communicator but also to a sophisticated noncoherent detector. By applying techniques developed in the paper to exploit the continuous-phase characteristic, an intercept receiver of reasonable complexity will perform appreciably better than traditional channelized detectors. >

Statistical models for evaluating the performance of noncoherent slow frequency-hopped M-FSK intercept receivers

Exact and approximate statistical models (analytical and simulation), based on average- and maximum-likelihood ratio tests, are studied and compared for the purpose of establishing an accurate assessment of the performance of noncoherent SFH M-FSK intercept receivers. Both continuous and discontinuous phase M-FSK cases are considered with important differences between the two. >

Carrier Tracking Loop Performance in the Presence of Strong CW Interference

In a coherent data link, narrow-band radio frequency interference (RFI) near the carrier frequency can degrade the link performance by impacting the carrier tracking loop behavior and producing a partial or complete loss of coherence. If the RFI is strong enough, this effect can occur even though the frequency of the interference lies well beyond the carrier tracking loop bandwidth. In 1973, Bruno and Bianchard independently performed similar analyses of the response of a phase-locked loop (PLL) to a continuous wave (CW) interferor, and derived conditions under which the loop drops carrier lock and tracks the interference instead. This paper compares the contributions of these two analysts, and extends Brunos closed form approximation for the loop phase error to the entire lock region.

Rain compensation algorithm for ACTS mobile terminal

The initial advanced communication technology satellite (ACTS) mobile terminal (AMT) demonstrations will involve two-way communications between the high-bit-rate link evaluation terminal (HBR-LET), which is a fixed terminal (FT), and a van-housed mobile terminal (MT). The HBR-LET has the capability of adjusting its transmitted uplink power over an approximately 10 dB range to compensate for forward uplink rain attenuation. However, because of size and weight limitations, the MET cannot use power control as a rain compensation technique. Consequently, the AMT rain compensation algorithm (RCA) is based on a formula for varying the transmitted data rate in either direction to maintain link performance within acceptable limits. The objective of the AMT RCA is to ensure reliable operation in both the forward and return directions despite the possibility of uplink or downlink fading due to rain events in the vicinity of the FT or MT. In particular, the RCA must maintain at least a 3 dB link margin at the highest possible transmission rate (AMT can operate at 9.6, 4.8, or 2.4 kb/s) permitted by the prevailing channel conditions. The 3 dB minimum link margin is a system design safety factor to accommodate conceivable implementation losses. >

Long Frame Sync Words for Binary PSK Telemetry

Correlation criteria have previously been established for identifying whether a given binary sequence would be a good frame sync word for phase-shift keyed telemetry. In the past, the search for a good K -bit sync word has involved the application of these criteria to the entire set of 2Kbinary K -tuples. It is shown that restricting this search to a much smaller subset consisting of K -bit prefixes of pseudonoise sequences results in sync words of comparable quality, with greatly reduced computer search times for larger values of K . As an example, this procedure is used to find good sync words of length 16-63; from a storage viewpoint, each of these sequences can be generated by a 5- or 6-bit linear feedback shift register.

Strategies for FH/MFSK Signaling with Diversity in Worst-Case Partial-Band Noise

Optimum diversity and worst-case partial-band noise jamming conditions have been derived for noncoherent energy detection of frequency-hopped (FH) M -ary frequency-shift keyed (MFSK) signals using a soft-chip decision suboptimum linear combining metric with perfect jamming-state side information. However, the assumption implicit in previous publications is that the error rate is first maximized over the jammers partial-band duty factor for arbitrary diversity, and the result is then minimized over the amount of diversity. This paper shows that if the order of optimization is reversed, different conditions and performance are produced; that is, the previous solution is not a saddlepoint. This introduces some game-theoretic considerations for the communicator and the jammer, the risks and advantages of which are explored.