In this paper, the problem of code acquisition for spread-spectrum systems is investigated in the presence of frequency errors. The classic approach of noncoherent post detection integration (NCPDI) is contrasted with differential post detection integration (DPDI), presented in two different versions, namely DPDI-Real and DPDI-Abs, respectively, suited for fine and large frequency offsets. The differential schemes are characterized thoroughly introducing a novel analytical treatment that is validated by simulations. In order to fairly quantify the potential gains introduced by the differential solutions, specific detector parameter optimization is performed for each scheme. The interesting result is that the DPDI significantly outperforms the classic NCPDI approach for large frequency errors, and behaves close to it for small offsets. DPDI can, thus, be considered as a very robust PDI solution with moderate complexity.

The orthogonal frequency division multiplexed (OFDM) system introduced here, termed interference suppressing OFDM (IS-OFDM), has the capabilities of suppressing narrowband interference in wideband wireless applications. The IS-OFDM encodes each transmitted symbol in all frequency bins. Each frequency bin then "contains" all transmitted symbols which are distinguished and separated from each other by orthogonal Hadamard sequences. The IS-OFDM can provide a point-to-point wireless link without spreading the incoming data rate. In addition, the IS-OFDM has all the advantages of the ordinary OFDM, which is shown to be a special case of the IS-OFDM. We present the IS-OFDM system design and evaluate its performance in the presence of narrowband interference and AWGN channel.

We present an ultra wide bandwidth (UWB) wireless network for in-home cordless networking and wireless distribution of cable TV channels. The article describes the network services, the media access control, the physical link transmitter and receiver design and the link bit error rate (BER) performance. The physical link is based on an interference suppressing OFDM (IS-OFDM) in which the total number of frequency bins (subcarriers) of the UWB channel is divided into groups. Every frequency bin in a group carries all transmitted symbols for that group which are distinguished and separated from each other by orthogonal Hadamard sequences. The proposed design may then suppress narrow-band interference which is often present in UWB channels. In an indoor multipath channel, IS-OFDM has also a significant advantage over ordinary OFDM, which, as shown, does not offer acceptable performance for this type of channel. The IS-OFDM link then is expected to satisfy the high bit rate needs and meet the required quality of service with a minimum transmit power so that it does not cause interference beyond the perimeter of the home.

In the paper, the preamble structure of IMT-2000 SW-CDMA air radio interface is considered in the evaluation of the performance of different post detection integration techniques for code acquisition in the return link of a satellite W-CDMA system. In particular, non-coherent post detection integration (NCPDI) and two different options of differential post detection integration (DPDI) techniques, namely DPDI-abs and DPDI-real, are investigated in terms of missed detection and false alarm probabilities. AWGN and Rician channels are considered in the presence of a frequency error. Both analytical and simulation results are provided.

In unknown channels, nonadaptive maximum likelihood sequence detection (NA-MLSD) is far from optimum in the presence of channel-induced uncertainty. To counteract this uncertainty, conventional solutions augment MLSD with external channel estimators. However, for very low SNR values this estimation procedure becomes marginal and the conventional adaptive MLSD (CA-MLSD) approaches perform poorly. We consider joint data decoding and parameter estimation techniques, and in particular per survivor processing (PSP) techniques, as a potentially effective solutions to this problem, at the expense of increased complexity. The performance/complexity tradeoff is addressed for a convolutionally encoded Q-PSK return link of an SHF/EHF satellite system for multimedia services impaired by phase noise and frequency offsets. By contrasting NA-MLSD, CA-MLSD, and PSP, ranges are provided for channel conditions where the tradeoff favors a particular technique. Further, CA-MLSD and PSP are also contrasted in terms of scalar/ vector estimation performance.

The application of per-suvivor processing (PSP) to digital satellite communications at Ka-band and beyond is considered. The PSP approach is used in a convolutionally encoded M-PSK transmission scheme to effectively counteract the degradations caused by phase noise and frequency offsets. Second order tracking loops are considered for per-survivor parameter estimation. A comparison is carried out between conventional adaptive maximum likelihood sequence detection (CA-MLSD) and PSP schemes both in terms of detection and estimation performance. Emphasis is placed on the analysis of the estimation quality one of the most unexplored research areas in the field of PSP-based systems. To this aim, novel definitions for a decision-related tracker and virtual tracker are introduced and their performance analyzed. Monte-Carlo simulations are provided to show the improvement in both estimation and detection quality brought about by PSP with respect to CA-MLSD.