Micro- and macrodiversity MDPSK on shadowed frequency-selectivechannels

The performance of M-ary differential phase shift keying (MDPSK) on frequency-selective slow Rayleigh fading, lognormal shadowed channels with diversity combining is analyzed for mobile and portable applications. The use of L-branch equal gain postdetection microdiversity combining to mitigate the effects of fading and P-port macrodiversity to alleviate the effects of shadowing are investigated. Four performance criteria are considered for a frequency-selective multipath fading, intersymbol interference channel. These are, the short term bit error rate (BER), the irreducible BER, the complementary distribution over the lognormal shadowing of the average BER, and the probability that the instantaneous BER exceeds a threshold value, averaged over a spatial environment. Closed-form expressions for the four performance criteria are obtained. The BER and outage performance results show that diversity combining is an effective method for improving the system performance (and hence system reliability), when the normalized delay spread is not large. It is also seen that, in most cases, 4DPSK gives the best performance followed by 8DPSK and 2DPSK, respectively, for a given information throughput     

Bit error probabilities of NCFSK and DPSK signals in microcellular mobile radio systems

Microcellular mobile radio systems are studied where the desired signal has Rician statistics and the cochannel interferers experience Rayleigh fading. The probability density function of the signal-to-interference ratio is derived and is used to obtain the bit error probabilities of noncoherent frequency shift-keying and differential phase shift-keying signals.<>     

Analysis of microdiversity and dual channel macrodiversity in shadowed fading channels using a compound fading model

Wireless channels are affected by short-term fading and long-term fading (shadowing). A compound fading model was proposed for the modeling of shadowed fading channels which resulted in a closed form solution for the probability density function (pdf) of the signal-to-noise ratio (SNR). This model is applied to a case where both micro- and macro-diversity schemes are implemented to mitigate short-term fading and shadowing, respectively. Using the compound fading model, it is shown that the pdf of the signal-to-noise ratio after the implementation of maximal ratio combining (MRC) at the micro level and selection combining (SC) at the macro level can be expressed in analytical form. Even when branch correlation exists, the pdf still can be expressed in analytical form. Thus, the compound pdf model offers significant improvement over approaches which use lognormal pdf for shadowing. The performance of a coherent binary phase shift keying (BPSK) modem is evaluated using this approach. The results demonstrate the simplicity and usefulness of the compound pdf in the performance analyses of shadowed fading channels even when branch correlation exists at the base station or correlation exists between base stations.     

Slow shadowing and macrodiversity in the Capture‐Division Packet Access (CDPA)

Recently, a new method for achieving spectrum reuse in cellular systems, called Capture‐Division Packet Access (CDPA), has been introduced. The method uses a single frequency in all cells, and exploits packet switching and packet retransmission as a means to overcome destructive cochannel interference. As the CDPA key factor is packet retransmission, it is also very effective in fighting lognormal shadowing attenuation as long as this attenuation can be considered independent from slot to slot. In this paper we analyze CDPA in presence of “slow shadowing”, to account for situations in which obstacles obscure the receiver for several transmission periods. The results show a severe throughput impairment with respect to the “fast shadowing” model. A variation of CDPA, Macrodiversity CDPA, that uses three corner fed antennas and three packet receivers is analyzed. The numerical results show that M‐CDPA is more efficient than CDPA and that it is only slightly affected by both fast and slow shadowing. To further investigate its robustness, a non‐lognormal slow shadowing model, the hard shadowing model, is also analyzed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Convolutional double accumulate codes (or double turbo DPSK)

We consider the serial concatenation of a convolutional code with two differential encoders (or accumulate codes). Simulations of such a concatenated scheme using a rate 1/2 outer convolutional code (sometimes punctured to increase the overall rate) show that, at high rates, the bit error rate (BER) and frame error rate (FER) performance of these codes is significantly better than a concatenation with only one accumulate code and a parallel concatenated convolutional code (PCCC) of similar complexity. An intuitive explanation for the performance of these codes is also given     

A Binary Noncoherent Frequency-Shift-Keying (NCFSK) Multiple-Message One-Shot Radio Transmission System that Uses a Sync Preamble

A binary noncoherent frequency-shift-keying (NCFSK) multiple-message one-shot radio transmission system is discussed where the receiver has no prior knowledge of the possible starting time of transmission. In this system each transmitted signal has a common preamble for signal acquisition and self-synchronization purposes. System design procedures are described for allowable frequency of occurrence of false alarm and probabilities of a miss and a message error specified for the system. In addition, the probability of premature response (i.e., the probability that the receiver makes an affirmative decision on acquisition of the signal when the sync preamble is only partially received) is taken into account. It is shown that the selection of sync preamble codes from randomly generated binary sequences can be a highly attractive approach. A simple, but very meaningful, criterion is suggested for aid in such a selection. The system described here can be used as a radio warning system and also as a selective call or selective interrogation system.     

Second‐order statistics of system with N‐branch microdiversity and L‐branch macrodiversity operating over gamma shadowed Nakagami‐m fading channels

The problem concerning short‐term fading and long‐term fading (shadowing) and their deleterious effects on wireless systems performance has been in focus for a long time. In this paper, motivated by the results of propagation measurements in land‐mobile and indoor‐mobile systems, and by the fact that gamma distribution can describe shadowing reliably, Nakagami‐m distribution is used to model the signal envelope and gamma distribution is used to model the average signal power. Receive diversity with maximal‐ratio combining and selection combining is implemented at the microlevel and macrolevel, respectively. The general case is explored, which assumes that microdiversity and macrodiversity are provided through arbitrary number of channels. Because shadowing has larger correlation distance than short‐term fading, correlated macrodiversity channels are studied. This paper investigates the dynamics of the received signal. A novel rapidly converging infinite‐series expression for average level crossing rate and average fade duration are obtained. Numerical results are graphically presented to examine the impact of fading severity, shadowing severity, number of diversity branches at the microlevel, number of base stations and correlation between base stations to the system's performance. Computer simulations are also performed to verify the validity and the accuracy of proposed theoretical analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

Tight bounds on the bit-error probabilities of 2DPSK and 4DPSK innonselective Rician fading

The bit-error probabilities (BEPs) of matched-filtered differentially detected two differential phase-shift keying (2DPSK) and 4DPSK over the nonselective Rician-fading channel are studied using the upper bound in Kam (1994). The bound coincides with the exact error probability result in the binary case and provides very accurate estimates of the BEP in the quadriphase case, especially for high signal-to-noise ratio (SNR) and small K-factor. The bound provides a simple analytical handle for studying the behavior of the error probability as a function of the Doppler spectrum, the Doppler bandwidth, and the K-factor. A new result is obtained for the irreducible error-rate floor. The results are useful for the design of digital mobile radio communication systems     

Impact of macrodiversity on capacity and coverage of cellular network

This paper proposes an analytical study of downlink macrodiversity. Considering a mobile in macrodiversity with two base stations, we first characterize and compute explicitely the load induced in a cell by downlink macrodiversity. We show that in most cases this load is positive, increasing the total cell load. We moreover show that the contribution of the macrodiversity to the cell load can be negative in the sense that the macrodiversity can increase the cell’s capacity. Afterward, we propose a new framework for the study of cellular networks called the fluid model which allows to calculate analytically that load. The key idea of the fluid model is to approximate the discrete base stations (BS) entities by a continuum of transmitters which are spatially distributed in the network. This allows us to obtain simple analytical expressions of the main characteristics of the network. In this paper, we focus on the downlink other-cell interference factor f, which we define here as the ratio of outer cell received power (i.e. the power received from other cells) to the inner cell received power. This fluid model allows calculating the influence of interference on any mobile in a cell, whatever its position. The fluid analysis we develop enables to calculate the load of a cell analytically, and to quantify the macrodiversity impact. We generalize our analysis, considering a macrodiversity with a great number of base stations of the network.     

Combined adaptive RAKE diversity (ARD) and coding for DPSK DS/CDMAmobile radio

A diversity combining scheme, adaptive RAKE diversity (ARD), is proposed for a differential phase-shift keying (DPSK) direct sequence code division multiple access (DS/CDMA) mobile communications system. The ARD scheme minimizes the mean squared errors in the diversity combiner output. This suppresses the effects of the interference only paths in the time window for path diversity combining. Bit error rate (BER) performances with the proposed ARD and conventional equal gain combining (EGC) schemes are evaluated through laboratory experiments and compared. Block error rate (BKER) performance with the ARD scheme is also evaluated experimentally. Based upon the BKER evaluation results, an error correction scheme is proposed that is suitable for error occurrence characteristics of ARD output     

Effect of microdiversity and correlated macrodiversity on outages in a cellular system

We focus on maximum ratio combining at each base station and switching between base stations (BSs) as a simple macrodiversity technique. We obtain analytical results for pointwise outage probabilities for systems using one or a combination of both techniques to cover a desired area, assuming a certain correlation model for the set of path losses of the links connecting a terminal to the receiving BSs. Pointwise outage probabilities are averaged over the entire region of interest to get an estimate of the outage in the desired region. A comparison of micro- and macrodiversity schemes in terms of the outage gives insights as to the tradeoff between the two forms of diversity in the design of a cellular system.     

Outage probability in mobile telephony with directive antennas and macrodiversity

Signal-to-interference ratio statistics for mobile telephony systems with hexagonal coverage areas, multiple interferers, and three-corner base stations are investigated. Corner base stations simultaneously reduce total interference (because of antenna directivity) and provide macrodiversity against shadow fading. Our results indicate that for 3 or 7 channel sets, with 2 tiers of interferers and typical system parameters (propagation exponent of 3.7 and lognormal spread of 8 dB), the improvement is on the order of 11 dB over a baseline arrangement which employs centrally located omnibase stations without macrodiversity. Additional considerations of blocking probabilities and average voice activity indicate possible further improvements.     

Effects of Rician fading and branch correlation on alocal-mean-based macrodiversity cellular system

In a macrodiversity cellular system, switching radio links between base stations cannot be done instantaneously. Thus, branch selection is usually based on the measurement of the slowly varying local-mean power rather than the rapidly varying instantaneous signal power. We offer an exact mathematical model to analyze the performance of a local-mean-based macrodiversity cellular system in a shadowed-Rician (desired)/shadowed-Rayleigh (interfering) channel. We investigate the impact of both fading (Rician or Rayleigh) and shadowing in terms of cochannel interference (CCI) probability. We also present an analytical model to incorporate the effects of branch correlation on macrodiversity systems     

Binary DPSK transmission over terrestrial and satellite links (Corresp.)

It has been observed previously that downlink noise correlation has no effect on the average error probability of a differentially phase shift keyed (DPSK) satellite system when the symbols are equiprobable. We show thai this observation holds for a satellite system exhibiting amplitude-modulation-to-amplitude-modulation (AM-AM) conversion effects and amplitude-modulation-to-phase-modulation (AM-PM) conversion effects. It is also shown thai noise correlation has no effect even when a constant phase error is caused by the delay line of the DPSK receiver in terrestrial and satellite links.     

Offset DPSK and a Comparison of Conventional and Symmetric DPSK with Noise Correlation and Power Imbalance

The bit error rate performance of binary DPSK with an arbitrary offset of the phase change vector is derived in the presence of noise correlation and power imbalance, and the special cases of conventional DPSK (0 phase change offset) and symmetric DPSK (pi/2phase change offset) are compared. Precise conditions are given for optimum offsets, and it is shown that, from a practical standpoint, conventional DPSK gives the optimum performance of any offset scheme, and outperforms symmetric DPSK by an order of magnitude and more in error rate when the noise correlation becomes significant. It is also found that performance improvement over conventional DPSK can be realized, provided the noise correlation is known, by making the bit decision regions in phase space unequal, thereby demonstrating that the MAP estimator for DPSK without correlation is no longer optimum when the noise is correlated.     

Trellis coded MDPSK in correlated and shadowed Rician fadingchannels

The performance of trellis-coded multilevel differential phase-shift keying (TC-MDPSK) signals in correlated and shadowed Rician fading channels is evaluated. The pairwise error probabilities of the TC-MDPSK signals in the channels are calculated directly and approximated asymptotically. The asymptotic expression can be put into a product form and used in a transfer function approach to estimate the error performance of TC-MDPSK. The bit error rate of TC-MDPSK is estimated by using a truncated form of the union bound and by an asymptotic expression. In the two examples considered, these formulas show fairly good agreement in both correlated and shadowed Rician channels and are at least 2-dB tighter in signal-to-noise ratio than the Chernoff bound in the correlated Rician channels. Asymptotic expressions for the error probability of uncoded MDPSK in both correlated and shadowed Rician channels are also obtained     

TD-SCDMA集群系统中部分宏分集组网前向容量分析

TD-SCDMA集群小区使用宏分集技术可以有效的克服大尺度衰落,保证信号质量。本文首先分析了在没有任何措施的前提下进行宏分集组网,但前向容量会随着宏分集基站数的增多而减少。在分析容量损失原因的基础上,我们进一步提出在终端利用Rake接收机对各路信号进行同步、相位调整,再进行最大比值合并,然后发送给用户,由此,前向容量大大提高。     

Comments on "On Binary DPSK Detection"

This brief correspondence notes the equivalence between the optimumM-ary DPSK receiver given recently by Park and another form of this receiver suggested earlier in the literature but not referenced in Park's paper.     

基于FPGA的DPSK调制解调器的全数字实现

调制解调技术是通信系统的灵魂,其性能直接影响到整个系统的通信质量。由于数字技术的大量应用,数字调制解调技术得到了广泛的应用。随着软件无线电思想的发展,将整个系统尽可能地集成于一个芯片的设计方法已经呈现出强大的发展潜力,成为系统设计发展的主要方向。基于这种思想,介绍一种在单片FPGA上实现的全数字DPSK调制解调器的设计方法。整个设计基于ALTERA公司的QUARTUS II开发平台,并用单片CYCLONE系列FPGA芯片实现。     

Effects of Rician faded and log-normal shadowed signals on spectrumefficiency in microcellular radio

An assessment of spectrum efficiency for a microcellular land mobile radio system is presented by considering the desired signal as (fast) Rician fading with (slow) log-normal shadowing and cochannel interfering signals as uncorrelated (fast) Rayleigh fading superimposed over (slow) log-normal shadowing. Spectrum efficiency is defined in terms of reuse distance, i.e., cluster size, traffic intensity, bandwidth of the system, and area of a cell by considering cochannel interference probability. The expression for cochannel interference probability is derived using appropriate path-loss law for microcells for four different cases: Rician plus log-normal desired signal and Rayleigh plus log-normal interfering signals; Rician desired signal and Rayleigh fading plus log-normal shadowing interfering signals; Rician desired signal and Rayleigh interfering signals; and both desired and interfering signals as Rician fading. The performance of a microcellular system is compared with that of a conventional macrocellular system