INTRODUCTIONThe significant success of first-generation signals in GPS has fostered continuing expectations for improved accuracy. Current modulation designs have been restricted to phase shift keying with rectangular spreading symbols (referred to here as PSK-R), duplicating early modulation designs for digital communications. As other sources of error diminish, contributions from noise and multipath start to dominate. But bandwidth limitations preclude further improvements that might be obtained using PSK-R modulations with faster keying rates. Also, increasing transmitted power to improve accuracy is expensive and has a limited effect on multipath performance. Receiver design strategies such as very wide-bandwidth receiver front ends and very small early -late spacing in code-tracking discriminators provide diminishing returns at increasing cost.In contrast, modulations designed specifically for radionavigation can outperform existing modulation designs while using the same or even less bandwidth and enabling simple transmitter and receiver designs. Further, more advanced modulations can better share existing frequency allocations with each other and with heritage signals, thus preserving spectrum. It remains important that modulations provide binary phase values, maintaining ease of signal generation (including multiplexing multiple signals onto a single carrier) and receiver processing. These binary PSK modulations can readily be extended to higher-order alphabets.A significant study of modulations other than PSK-R for GPS was instigated by the need to modernize the military GPS service, adding a new military signal within the radio frequency (RF) bands already being used [1]. The binary offset carrier (BOC) modulation was developed for this purpose [2]. It has been found to provide the best overall performance [3], and is being implemented on Block IIR-M and Block IIF satellites to be launched as early as 2003. While BOC modulations were developed to provide spectral isolation from heritage signals modulating the same carrier frequency, it was quickly determined that they offer performance advantages as well. More recent work suggests that BOC modulations may allow yet another signal, in addition to heritage signals and the new military signal, to be added to currently allocated GPS bands [4]. While there has been previous consideration of subcarrier modulations for civilian signals (e.g., [5] mentions a C/A-code signal variant equivalent to a BOC(1,1)), this paper provides the first comprehensive discussion of BOC modulations in general, also demonstrating their enhanced performance and assessing their characteristics.The next section summarizes essential characteristics of BOC modulations. It defines the modulations, outlines the approach for generating them, and presents expressions for their second-order statistics. The third section introduces some example BOC modulations of particular interest, defines measures for evaluating characteristics of modulations for radionavigation, and evaluates these meas...

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development and analysis of signal processing for communications, navigation, radar, and other applications. He developed the Binary Offset Carrier modulation for the GPS M code signal, and more recently has been contributing to theoretical predictions of receiver performance. During 1998 and 1999, he led the GPS Modernization Signal Design Team's Modulation and Acquisition Design Subteam, contributing to many aspects of the signal design and evaluation. He has authored many technical papers and reports on theory and applications of signal processing. ABSTRACTTesting the response of C/A code receivers to partial-band interference (continuous Gaussian interference whose power is concentrated in part of the front-end bandwidth) has included examining how receivers measure and report the effect of such interference. This paper considers two fundamentally different ways that receivers measure and report the effect of interference on signal quality, demonstrating that in non-white noise the measures are not the same. While the effective C N / 0 reliably measures the effect of interference on a receiver, the precorrelation C N / 0 is not reliable. Specifically, precorrelation estimation of N 0 does not properly account for the spectrum of the interference. Depending on the spectrum of the interference, precorrelation estimates may be accurate, or may overestimate the degradation caused by interference, or may underestimate the degradation caused by interference. Theoretical and numerical results are provided and compared to some measured data.

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