Mark Walter Chamberlain

A 600 bps MELP vocoder for use on HF channels

The US government has developed and adopted a new military standard vocoder (MIL-STD-3005) algorithm called mixed excitation linear prediction (MELP) which operates at 2.4 kbps. The vocoder has good voice quality under benign error channels. However, when the vocoder is subjected to a HF channel with typical power output of a manpack radio (MPR), the vocoder speech quality is severely degraded. Harris has found that a 600 bps vocoder provides significant increase in secure voice availability relative to the 2.4 kbps vocoder. This paper describes a 600 bps MELP vocoder algorithm that takes advantage of the inherent inter-frame redundancy of the MELP parameters. Data is presented showing the advantage in both diagnostic acceptability measure (DAM) and diagnostic rhyme test (DRT) with respect to SNR on a typical HF channel when using the vocoder with a MIL-STD-188-110B waveform.

A software defined HF radio

Software defined radio (SDR) is a new approach for military radio systems. This new radio paradigm supports multiple channels with simultaneous waveforms, providing a new level of scalability and flexibility to the user, and allows for rapid technology insertion as it becomes available. This paper explores the insertion of legacy high frequency (HF) waveforms to one channel of a software defined radio with a focus on manpack radio (MPR) specific needs. The paper includes both software and hardware aspects of the complete radio system design. The paper will investigate hardware technology limits with respect to size, weight, power consumption, cost, and radio performance. The paper will look at the unique aspects of the HF communications that directly affect the software defined radio architecture.

Proposed data link protocol enhancements for STANAG-4538

The current NATO standard STANAG-4538 provides reliable data communications to support E-mail and many other types of IP applications. This standard is very tolerant to the sometimes harsh HF radio communication channels experienced by the war fighter. However, the protocol currently is limited by the choice of the raw high data rate waveform chosen when the HF channel improves. The paper visits several waveform level improvements that provide better throughput and lower latency than the current waveforms when SNRs and channel conditions allow. Simulation data is presented of the enhanced data link protocol with the existing NATO STANAG-4538.

HF data link protocol RF simulator performance based on STANAG 4538 and STANAG 4539

STANAG 4538 (S4538) defines a pair of ARQ protocols that provide error free data transfer between HF terminals or nodes. These protocols utilize a form of code combining to automatically adapt to the conditions of the HF channel. The achievable throughput of these data link protocols is limited by the choice of the underlying waveform. STANAG 4539 (S4539) defines a set of high data rate HF modem waveforms that provide on-air data rates up to 12,800 bps. The data link protocols developed by Harris Corporation and discussed in this paper, HDL+, apply the code combining concepts to the higher capacity data waveforms of S4539. HDL+ is currently being considered by the NATO HF radio ad hoc working group as an enhancement to S4538. The paper begins with an overview of the current definition of HDL+ highlighting several waveform level improvements that provide better throughput and lower latency than existing standard approaches, when channel conditions allow. The paper continues by presenting throughput performance measured on the AN/PRC-150C HF tactical radio using a hardware RF channel simulator setup comparing HDL+ with the data link protocol defined in S4538. The paper also presents comparison data of IP message load versus message delivered for a simple mesh network using the same RF simulator setup.