New results on the capacity of M-ary PPM ultra-wideband systems

Abstract

Abstract-In this paper, some new results on the capacity of a typical M -ary pulse position modulation (M -PPM) time hopping (TH) Ultra-Wideband (UWB) system are presented. Previous results using a "pure PPM model" are proven to exaggerate the real capacity of a UWB system. Based on an extended model containing correlator and soft decision decoding, the capacity is evaluated in the single-user case and in the case of a system with asynchronous multiple user interference (MUI) when the inputs are equiprobable. It is found that only when bit-signal-to-noise ratio (bit-SNR) is high enough, larger M leads to higher capacity; and for a specific M , the optimal values of PPM time offset parameter T d , which maximize the capacity, are independent of bit-SNR. The influence of MUI on capacity is detrimental, especially in the case of high bit-SNR.

Performance analysis of space-time codes in realistic propagation environments: A moment generating function-based approach

“…The obtained capacity expressions are independent of the shape of the used pulse. However, the results based on this pure PPM model actually exaggerate the capacity of a UWB system as shown in [11]. To bound the capacity more tightly, new models should be constructed to reflect all critical components of a UWB system.…”

Conditions and Performance of Ideal RAKE Reception for Ultra-Wideband Signals in Lognormal Fading Channels

“…So OPPM is not applicable to TH-UWB without further design considerations. For overlapped PPM, the optimal modulation parameter is smaller than the width of a pulse because the values of the pulse's autocorrelation could be negative [14]. The other modulation methods cause little time jitter.…”

“…The mean SEP can be evaluated numerically via Monte Carlo simulation with (14). An alternative way can be used to arrive at an explicit expression, considered next.…”

Hard-Input–Hard-Output Capacity Analysis of UWB BPSK Systems With Timing Errors

“…The maximum value of (9) is achieved when the system has equally likely input symbols in the binary modulation scheme [10], [19]. Therefore, the channel capacity for the desired user can be calculated as…”

“…For the same system, authors in [9] showed that the channel capacity is highly affected by pulse shapes. By modeling the multiple access interference (MAI) as Gaussian, the analysis on the channel capacity was extended to AWGN channels with multiple users in [10] - [13]. In [14], the channel capacities of pulse amplitude modulation (PAM) and PPM were compared over AWGN channels, where the MAI was also modeled as Gaussian.…”