Performance Evaluation of Access Channel Slot Acquisition in Cellular DS/CDMA Reverse Link

In this paper, we consider the acquisition performance of an IS-95 reverse link access channel slot as a function of system design parameters such as postdetection integration length and the number of access channel message block repetitions. The uncertainty region of the reverse link spreading codes compared to that of forward link is very small, since the uncertainty region of the reverse link is determined by a cell radius. Thus, the parallel acquisition technique in the reverse link is more efficient than a serial acquisition technique in terms of implementation and of acquisition time. The parallel acquisition is achieved by a bank of N parallel l/Q noncoherent correlators. The output characteristics of an l/Q noncoherent correlator are analyzed for band-limited noise and the Rayleigh fast fading channel. The detection probability is derived for multiple correct code-phase offsets and multipath fading. The probability of no message error is derived when rake combining, access channel message block combining, and Viterbi decoding are applied. Numerical results provide the acquisition performance for system design parameters such as postdetection integration length and number of access channel message block repetitions in case of a random access on a mobile station.     

Noncoherent hybrid parallel PN code acquisition for CDMA mobilecommunications

This paper proposes a noncoherent hybrid parallel pseudonoise (PN) code acquisition scheme for code-division multiple access (CDMA) mobile communication systems and analyzes the effect of multiple access interference (MAI) on the code acquisition performance for Rayleigh and Rician fading channels. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time slightly inferior to that of the total parallel acquisition in the case of severe MAI; on the other hand, it provides the flexibility in the tradeoff between the mean acquisition time and system complexity if no MAI is considered. The closed-form expressions of the detection and false-alarm probabilities and mean acquisition time are derived. Numerical analysis quantifies the severe performance degradation of code acquisition due to both MAI and channel fading, and demonstrates the dependence of the increase of mean acquisition time (due to MAI) on the number of users in the CDMA system, system design parameters, and channel fading statistics     

Effects of multiple threshold values for PN code acquisition inDS-CDMA systems

A decision method using multiple threshold value for PN code acquisition in DS-CDMA systems is describe. This technique is applied to a conventional hybrid search algorithm and analysis in terms of the probability of detection and false alarm. Simulation results show that the proposed scheme outperforms the conventional scheme in terms of detection probability because multiple threshold values mitigate any possible decline in performance caused by the used of a single threshold     

Performance of a class of parallel spread-spectrum code acquisitionschemes in the presence of data modulation

An acquisition procedure for data-modulated direct-sequence spread-spectrum systems is investigated. The correlation time is partitioned into subintervals, and the integration results in these subintervals are noncoherently combined for detection. The tradeoff between noncoherent combining loss and data modulation degradation guides the optimum choice of the number of subintervals. Two forms of data modulation are considered, namely, the alternate-data and random-data cases. The parallel acquisition schemes discussed allow multiple code-phase offsets to be examined at each test. The circular state diagram approach is used to analyze the performances of these schemes. The theory presented is valid for a class of such parallel schemes     

Direct-sequence spread-spectrum parallel acquisition in a fadingmobile channel

A parallel acquisition scheme for direct-sequence spread-spectrum systems is proposed, and its mean acquisition time performance is analyzed in both nonfading and Rayleigh-fading environments. An expression for the mean acquisition time is derived in terms of the probabilities of detection, missing, and false alarm. These parameters are first analyzed for a typical AWGN (additive white Gaussian noise) channel, then the Rayleigh-fading channel encountered in a typical UHF or microwave land mobile radio channel is studied. The channel is assumed frequency nonselective, and the effect of data modulation and code Doppler is not considered. The performance of the parallel system is compared to the corresponding serial system, and it is shown that a significant improvement can be achieved     

Rapid Acquisition for Direct Sequence Spread-Spectrum Communications Using Parallel SAW Convolvers

In this paper, a technique is described which uses multiple surface acoustic wave (SAW) devices in parallel to reduce the acquisition time of a direct sequence spread-spectrum communication system. Analysis of system performance in both the search and lock modes is presented, and key quantities such as probability of false alarm, probability of correct detection, mean dwell time, and mean time to lose lock are derived.     

Spread Spectrum PN Code Acquisition Using Hybrid Correlator Architectures

A hybrid correlator architecture is described which combines the serial structure of an active correlator with the parallel structure of a matched filter correlator. The mean PN code acquisition time performance of this hybrid serial-parallel correlator structure is analysed. Results are shown which compare the acquisition performance of the serial, parallel, and serial-parallel structures. The results are for a PN code length of 64 code chips and assumes a Gaussian channel with the receiver detection threshold set to obtain a constant false alarm rate. An enhancement to the serial-parallel acquisition algorithm is also described which can increase the acquisition time performance by about 15% for typical operating conditions. Overall the results demonstrate that the hybrid correlator can provide rapid code acquisition with a limited receiver complexity.     

Performance Limits in DS-CDMA Timing Acquisition

This paper addresses timing acquisition aspects in direct-sequence code division multiple access (DS-CDMA) systems. Various chip waveform shaping schemes are considered, including both one-chip long full-response pulses, and partial-response ones occupying several chip periods. Different figures of merits are considered in a comparative analysis that seeks to establish performance limits in terms of correct timing detection capability, false alarm rate, bandwidth occupancy, multiple-access interference (MAI), and inter-chip interference (ICI). A waveform design algorithm is formulated to optimize system performance in terms of signal-to-interference-ratio (SIR) subject to other signalling constraints, and a solution based on the use of prolate spheroidal wave functions (PSWF) is derived. Numerous waveform design examples are then constructed to illustrate acquisition detection capability versus system load for both faded and unfaded cases. A comparative assessment of the performance of conventional signalling waveforms against the optimized ones is also presented. In particular, the numerical results show that the half-sine pulse used in minimum shift keying (MSK) is quasi-optimal within the full-response category, while root-raised cosine (RRC) Nyquist filtering with 22% rolloff (used in third generation CDMA standards) is also close to optimal when considering many-chip-long pulses.     

Parallel code acquisition technique for preamble search in the CDMAreverse link

A parallel PN code acquisition technique for slotted-mode preamble search in a CDMA reverse link is presented. For received PN codes with different signal-to-noise ratios (SNRs), this scheme provides a sub-optimal threshold value such that the mean acquisition time is minimised     

Serial acquisition performance of single-carrier and multicarrier DS-CDMA over Nakagami-m fading channels

We investigate the issue of pseudo noise (PN) code acquisition in single-carrier and multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) systems, when the channel is modeled by frequency-selective Nakagami-m (1960) fading. The PN code acquisition performance of single-carrier and MC DS-CDMA systems is analyzed and compared when communicating over Nakagami-m fading channels under the hypothesis of multiple synchronous states (H/sub 1/ cells) in the uncertainty region of the PN code. In the context of MC DS-CDMA, the code acquisition performance is evaluated, when the correlator outputs of the subcarriers associated with the same phase of the local PN code replica are noncoherently combined by using equal gain combining (EGC) or selection combining (SC) schemes. The performance comparison of the above mentioned schemes shows that the code acquisition performance of the MC DS-CDMA scheme, especially when using the EGC scheme, is more robust, than that of single-carrier DS-CDMA schemes communicating over the multipath Nakagami-m fading channels encountered. However, our code acquisition performance comparison also shows that if the detection threshold was set inappropriately, the performance might be degraded, even if the channel fading becomes less severe.     

Common packet data channel (CPDC) for integrated wireless DS-CDMAnetworks

A common packet data channel (CPDC) architecture is proposed to support bursty, packet-based services in direct sequence code-division multiple-access (DS-CDMA) integrated wireless access networks. The architecture employs an asynchronous transfer mode (ATM) strategy in the forward CPDC link and a spread ALOHA-type random access strategy in the reverse CPDC link. A congestion control algorithm using base station broadcast and portable terminal random delay call reattempt is described. A performance analysis of the CPDC architecture and algorithms is carried out, and formulas for the bit error rate, blocking probability, system delay time, transmission time, and waiting time for packet data calls are derived. The interference caused by a CPDC to stream services in the network is determined, and the capacity of a CPDC is evaluated in terms of the number of packet data subscribers that can be served with a specified grade of service (GOS)     

Performance Analysis of MIMO Based CDMA Code Acquisition Over Rayleigh Fading Channels

This paper proposes a new MIMO based CDMA code acquisition scheme. The pilot codes consist of a number of short Gold code sequences which are transmitted in parallel using a group of transmit antennas. Reception diversity is performed by multiple receive antennas at the receiver. Three different acquisition detection techniques are proposed and compared. Corresponding threshold optimizations are investigated as well. Detection and false alarm probabilities are derived in closed form based on the outputs of non-coherent matched filters. The acquisition performance is evaluated in terms of mean acquisition time (MAT) in Rayleigh fading environment. It is shown that the proposed MIMO acquisition scheme exhibits a much better MAT performance than the conventional single-antenna acquisition scheme. The results reveal that multiple receive antennas can be utilized to significantly reduce the MAT at the expense of receiver complexity increase. On the other hand, increasing the number of transmit antennas makes the MAT performance more robust in the presence of strong interference.     

A Theoretical Evaluation of Parallel Interference Cancellation in M-Ary Orthogonal Modulated Asynchronous DS-CDMA System Over Multipath Rayleigh Fading Channels

In this paper, we tackle the problem of theoretical evaluation for the multistage parallel interference cancellation (PIC) scheme in a direct-sequence code division multiple access (DS-CDMA) system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time varying multipath Rayleigh fading channel. By applying the Central Limit Theorem and some other approximations to multiple access interference (MAI) and intersymbol interference (ISI), as well as assuming identically distributed chips from a single interferer, the bit error rate (BER) performance of the PIC scheme at any stage can be recursively computed from the signal-to-noise ratio, number of users, the number of path per user, processing gain of the CDMA system, and the average received power of each path. For completeness, the BER expression is derived for chip synchronous and chip asynchronous systems over both equal and unequal power multipath channels. The proposed analysis is validated by the Monte Carlo simulations and proved to be reasonably accurate, and it gives insight into the performance and capacity one can expect from PIC-based receivers under different situations. For instance, the analytical results can be used to examine the convergence property, multipath diversity gains, and near-far resistance of the PIC scheme.     

Code acquisition in transmit diversity DS-CDMA systems

In this paper, two code acquisition schemes are studied for use in conjunction with transmit diversity direct-sequence code-division multiple access (DS-CDMA). One is a training-based single-user maximum-likelihood (SUML) estimator, which can achieve code acquisition very fast at low computational complexity. The other is a blind estimator based on the multiple signal classification (MUSIC) algorithm. Two recently proposed transmit diversity schemes known as orthogonal transmit diversity simulcast (OTD-S) and space-time selective spreading transmit diversity (STSTD) are considered. While the advantages of transmit diversity from the detection standpoint are well known, less is known about how code acquisition performance is affected by the use of transmit diversity. Through the analysis in this paper, it is proven that the SUMI. estimator should give the same performance in both the OTD-S and STSTD schemes in a single-user environment. In a multiple-user environment, simulation results show that the STSTD system offers slightly better code acquisition performance. It is also seen that the SUML estimators provide significantly better code acquisition performance than the MUSIC estimators in either transmit diversity system. From the standpoint of robustness to carrier frequency offset, it Is found that the training-based SUML estimator is very sensitive to frequency offset, while the MUSIC estimator is quite robust. A simple frequency offset estimator to be used in conjunction with the SUML estimator is also proposed and is shown to make the timing estimator quite tolerant of substantial frequency offsets.     

Dispersion Effects in Millimeter-Wave Fiber-Radio Systems Employing Direct-Sequence Code Division Multiple Access

We investigate the impact of fiber chromatic dispersion on the performance of an externally modulated millimeter-wave fiber-radio system incorporating a broadband radio direct-sequence code division multiple access (DS-CDMA) scheme. In particular, we investigate the effect of dispersion on DS-CDMA signals with regard to CDMA code rate, center frequency, and modulator chirp. We show that the spreading of the signal spectrum using DS-CDMA can result in significant reductions in data amplitude variations normally experienced in externally modulated millimeter-wave fiber-radio systems. We also demonstrate the successful transmission of a 10-Mb/s data channel over a 39-GHz fiber-radio link employing DS-CDMA and consisting of 25 km of standard optical fiber and a 1-m radio link.     

Successive Interference Cancelers for Multimedia Multicode DS-CDMA Systems Over Frequency-Selective Fading Channels

Noncoherent and coherent multicode direct-sequence code-division multiple access (DS-CDMA) systems with successive interference cancellation (SIC) for multimedia reverse links over frequency-selective fading channels are studied. Followed by a RAKE receiver, the SIC scheme is applied for combating the multiple access interference. The bit error rate (BER) using the SIC technique over Nakagami-m fading channels is derived. Simulation results show that the multicode DS-CDMA system with SIC has demonstrated better performance than that without SIC under the multipath fading environment, while their corresponding numerical results from performance analyses are also provided for verifications. Furthermore, the coherent receiver could achieve a more satisfactory BER than the noncoherent counterpart at the expense of synchronization.     

基于分段相关－视频积累方法的多驻留伪码捕获系统优化设计

针对载波多普勒下的伪码捕获问题,分析了基于分段相关-视频积累方法的多驻留伪码捕获系统的最优性能。推导了正交双通道检测器的检测概率和虚警概率表达式,给出了多驻留系统的捕获时间均值表达式;通过采用遗传算法对系统进行优化设计,增大了系统的多普勒容限,降低了捕获时间;分析了驻留级数、多普勒和载噪比等对捕获系统性能的影响。研究成果可用于指导扩频系统接收机伪码捕获模块的设计。     

Allocation policies of quasi-orthogonal codes on the forward link of a multicarrier DS-CDMA system

Abstract-Alternative code assignment policies for the forward link of a multicarrier DS-CDMA system employing the recently proposed quasi-orthogonal sequences are put forth in this letter. It is demonstrated how different allocation strategies of quasi-orthogonal codes alter the interference level suffered by active units; it is also shown how to shape the rate of interference growth as a function of the number of active users within the reference cell, implementing some specific code allocation patterns. The performance achieved by various schemes is assessed in a frequency selective fading environment, in terms of average bit error probability.     

Space time frequency coding for dual polarization MIMO in hybrid mobile satellite system

The hybrid mobile satellite system operating in a single frequency network （SFN） mode is increasingly becoming attractive. The combination of satellite component （SC） and terrestrial component （TC） promises a better quality of service （QoS）. Multimedia broadcast and multicast services （MBMS） are expected to be prevailed in this kind of system. Several space frequency （SF） or space time （ST） codes have been proposed to enhance the system performance due to the lack of reverse link and omni-directional transmission. However, they mostly consider the system with only one SC and one TC and fail to make full use of available diversities. This paper presents a novel way to realize the dual polarization multiple input multiple output （MIMO） transmission by using the space time frequency （STF） code. The theoretical analysis and simulations indicate that the application of STF code can improve the system performance dramatically. A higher diversity gain can be achieved due to the cooperative transmission of SC and TC, while the coding gain can be enhanced by the reusing of STF code between SCs or TCs. Even if some of the links are lost, it can still work properly and benefit from the STF code. The relative relay can result in a degradation up to 0.5 dB in the coding gain.     

Rapid acquisition algorithms for synchronization of burstytransmissions in CDMA microcellular and personal wireless systems

Two rapid synchronization acquisition algorithms applicable to spread spectrum links of code division multiple access (CDMA) personal communication systems are proposed and evaluated. The algorithms operate within a self-referencing matched filter synchronizer structure, and are particularly useful in reducing synchronization overhead on links designed to carry packet-type services. The main distinguishing characteristic between the two schemes is that one uses hard-decision while the other uses soft-decision detection. The proposed schemes are especially applicable to reverse link transmissions in quasisynchronous CDMA systems in which timing at portable terminals is established via pilot and synchronization signals received on respective code-division channels from the home base. If discontinuous (bursty) transmission is used on reverse links, the acquisition process is required for each transmission burst because of the propagation time uncertainty. Analysis of the algorithms on additive white Gaussian noise (AWGN) and Rayleigh fading channels reveals that their performance depends significantly on the choice of synchronizer parameters and the average despread signal-to-interference ratio (SIR). When this choice is proper, acquisition over a single preamble of relatively short duration can be achieved with high probability. The soft-decision scheme introduces a performance advantage of between 4-9 dB depending on the length of the synchronizing preamble