Combined Transmitter Diversity and Multi-Level Modulation Techniques

Orthogonal transmitter diversity such as frequency diversity and time diversity is quite simple to implement and, with optimum signal combining, can take full advantage of fading multipath channels. However, such a scheme has a bandwidth efficiency that decreases inversely with the number of diversity branches making it less attractive in wireless communications applications. This paper considers combined orthogonal transmitter diversity and multi-level linear modulation techniques. The idea is to view the signal constellations of the modulation scheme in an augmented signal space formed by the modulation signal dimension and the number of branches of the transmitter diversity scheme. This augmented signal space provides a good spread for the modulation signal points and can be quite efficient for high-level linear modulation techniques. The obtained results show that this combined scheme, not only improves the system performance on both additive white Gaussian noise and fading multipath channels, but also improves the bandwidth efficiency of orthogonal transmitter diversity.     

Multicarrier-Based QAPM Modulation System for the Low Power Consumption and High Data Rates

Low power consumption and high data rate are the most important requirements for the communication system. Especially, very low power consumption modulation method is required for the short range communication systems such as the medical implantable communication devices or capsule endoscope, and so on. For the higher data rate, we like to combine the OFDM system into the QAPM since the OFDM system has higher bandwidth efficiency than a single-carrier system. In this paper, we like to propose a QAPM (Quadrature amplitude position modulation) method combined with the orthogonal frequency-division multiplexing (OFDM) system. Next, we analyze the performance of three low-power-consumption modulation schemes: the phase shift position modulation (PSPM), phase silence shift keying (PSSK), and QAPM using orthogonal frequency-division multiplexing (OFDM) system in the multi-path channel. These schemes have lower bandwidth efficiency and the higher power efficiency than the existing phase-shift keying (PSK) and quadrature amplitude modulation (QAM) schemes. It can be shown that they can achieve greater power efficiency because every modulation symbol has a zero-envelope period as in pulse-position modulation (PPM) techniques. Finally, we compare the performances of the PSPM, PSSK, and QAPM modulation combined with the OFDM system with regard to bit error rate performance and throughput.     

Modulation and Coding for Noncoherent Communications

Until recently, the theory of noncoherent communications was premised on the use of orthogonal multi-pulse modulation such as frequency shift keying. The main drawback of this modulation scheme has been its poor spectral efficiency (rate/bandwidth). This paper considers instead the more general non-orthogonal multi-pulse modulation (NMM) technique. Optimal and suboptimal noncoherent detection strategies for NMM are reviewed and their asymptotic (high SNR) performances are characterized for the additive Gaussian as well as the Rayleigh fading channels. The resulting non-Euclidean distance measures are then used to design NMM signal sets that yield significantly higher bandwidth efficiencies than their orthogonal counterparts. NMM in conjunction with convolutional coding is also studied as a way to improve energy efficiency. Several optimal convolutional codes are examined together with our signal designs. An introduction to equalization on the noncoherent channel is also presented and illustrated by example. This paper thus contains several new results and attempts at the same time to give a tutorial exposition of the subject of noncoherent communications.     

A New Modified MPPM for High‐Speed Wireless Optical Communication Systems

Previous work proposed combining multipulse pulse position modulation (MPPM) with pulse amplitude modulation to form multipulse amplitude and position modulation (MPAPM), which is a hybrid modulation that results in an improvement in bandwidth efficiency but a degradation in power efficiency. In this paper, to achieve greater power efficiency and a better data rate, we propose multipulse dual amplitude‐width modulation, based on MPAPM and pulse width modulation. The proposed scheme shows a remarkable improvement in data rate and a 1.5‐dB improvement in power efficiency over MPAPM, while sustaining the bandwidth efficiency. After introducing symbol structure, we present the theoretical expressions of spectral efficiency, the power requirements, and the normalized data rate, as well as the results of comparing the proposed modulation to MPPM and MPAPM.     

New Optimal and Suboptimal Resource Allocation Techniques for Downlink Non-orthogonal Multiple Access

This paper investigates several new strategies for the allocation of radio resources (bandwidth and transmission power) using a non-orthogonal multiple access (NOMA) scheme with successive interference cancellation (SIC) in a cellular downlink system. In non-orthogonal access with SIC, the same subband is allocated to multiple users, which requires elaborate multiuser scheduling and subband assignment techniques, compared to orthogonal multiplexing. While taking into account various design issues, we propose and compare several optimum and suboptimum power allocation schemes. These are jointly implemented with multiple user scheduling strategies. Besides, a minimization of the total amount of used bandwidth is targeted. Also, to increase the total achieved system throughput, a hybrid orthogonal-non orthogonal scheme is introduced. This hybrid scheme enables a dynamic switching to orthogonal signaling whenever the non-orthogonal cohabitation in the power domain does not improve the achieved data rate per subband. Extensive simulation results show that the proposed strategies for resource allocation can improve both the spectral efficiency and the cell-edge user throughput, especially when compared to previous schemes employing either orthogonal signaling or NOMA with static inter-subband power allocation. They also prove to be robust in the context of crowded areas.     

无线光通信中的脉冲位置宽度调制技术

针对无线光通信系统中L级脉冲位置调制(PPM)技术带宽效率较低的问题,结合L级脉冲位置调制技术和L级脉冲宽度调制(PWM)技术,提出了L级脉冲位置宽度调制(PPWM)技术.该调制技术通过适当降低功率效率提高了带宽效率,分析了PPWM技术的功率效率和带宽效率,在弱湍流信道模型下分析了PPWM调制技术的误包率,并与其他调制技术进行了比较.结果表明L级脉冲位置宽度调制技术具有低误码率,高功率效率、高带宽效率和较低误包率等优点.     

A bandwidth-power efficient modulation scheme based on quaternary quasi-orthogonal sequences

A novel modulation scheme suitable for noncoherent demodulation based on quaternary quasi-orthogonal sequences is proposed. Compared to orthogonal modulation, the controlled quasi-orthogonality between the sequences allows significantly increased bandwidth efficiency with little or no degradation in power efficiency. A hardware efficient demodulator structure using fast Walsh transforms is also presented.     

一种高效的混合M元扩频通信方案

为进一步提高扩频通信系统的频带利用率和抗截获性能,将正交扩频技术与码相位循环移位调制技术相结合,提出了一种新的高效多进制扩频通信方案。在正交信道的每条支路上,首先采用M元双正交扩频调制,再以每一个扩频码为原型码进行码相位循环移位调制,选用专用的伪噪声码进行同步,在接收端用基于变换域处理的循环相关器进行解扩。计算机仿真表明,该方案易于实现同步,同时有较高的频带利用率和更强的抗截获性能。该方案在卫星隐蔽通信、数据链通信等领域有较大的应用价值。     

A Two-Point Modulation Technique for CMOS Power Amplifier in Polar Transmitter Architecture

A two-point modulation technique is presented that improves the performance of nonlinear power amplifiers (PAs) in polar transmitters. In this scheme, the output amplitude modulation is performed by controlling the current of the PA. The current control technique enables the PA to provide wideband amplitude modulation, as well as high power control dynamic range. In addition, the supply voltage of the PA is adjusted based on the output power level. The voltage supply adjustment substantially improves the effective power efficiency of the PA. The voltage supply control is performed using a second-order sigma-delta dc-dc converter, which presents an efficiency of over 95% in its operational range. The PA operates at 900 MHz with maximum output power of 27.8 dBm and power efficiency of 34% at maximum output power. The proposed PA achieves 62-dB power control dynamic range with amplitude modulation bandwidth of over 17.1 MHz. The circuits are fabricated in a CMOS 0.18 mum process with a 3.3-V power supply.     

Signal space diversity: a power- and bandwidth-efficient diversitytechnique for the Rayleigh fading channel

The increasing need for high data-rate transmissions over time- or frequency-selective fading channels has drawn attention to modulation schemes with high spectral efficiency such as QAM. With the aim of increasing the “diversity order” of the signal set we consider multidimensional rotated QAM constellations. Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, This multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense     

Differential detection of quadrature frequency/phase modulatedsignals

This paper proposes a pilot-symbol-assisted (PSA) signaling format that enables the differential detection of the differentially phase-encoded quadrature frequency/phase modulated (NDQFPM) signal using N orthogonal frequencies. The PSA-NDQFPM signal is transmitted on a frame-by-frame structure. The channel considered is an additive white Gaussian noise channel where the channel phase varies so slowly that it is assumed constant over one frame duration. Each frame consists of J NQFPM pilot symbols and I data blocks, each containing L NDQFPM symbols, with the first symbol differentially phase encoded with respect to pilot symbols. Based on the maximum-likelihood sequence estimation principle, the maximum-likelihood differential-detection (ML-DD) algorithm is developed to detect the PSA-NDQFPM signal on a block-by-block basis. Tight upper and asymptotic bounds are derived and verified by simulation to evaluate the bit error performance of the ML-DD algorithm. Both bandwidth and power efficiencies of PSA-NDQFPM with ML-DD are compared to NQFPM with coherent detection, constant-envelope NQFPM with coherent detection, constant-envelope NDQFPM (also known as NFSK/4DPSK) with ML-DD, and conventional 2DQFPM (also known as DQ²PSK) with ML-DD. It is analytically shown that PSA-NDQFPM with ML-DD has lower power efficiency than NQFPM with coherent detection and NFSK/4DPSK with ML-DD, but still can provide noticeably higher power efficiency than DQ ²PSK with ML-DD when a medium frame length is used. Due to the use of pilot symbols, PSA-NDQFPM with a medium frame length has marginally lower bandwidth efficiency than its coherent counterpart NQFPM, but still yields significantly higher bandwidth efficiency than constant-envelope NQFPM and NFSK/4DPSK     

A Multilevel Coded Modulation Approach for Hexagonal Signal Constellation

We propose a new coded modulation called hexagonal shell modulation (HSM). The HSM has a signal constellation composed of shell-like tiling of hexagons and thus has a lower peak-to-average power ratio (PAR) than a standard square quadrature amplitude modulation (QAM) with comparable bandwidth efficiency and minimum Euclidean distance. The main challenge is that HSM has a non-power-of-two number of constellation points, and thus assignment of binary information to HSM is not straightforward. We resolve this by applying a multilevel coded modulation (MLC) scheme where a ternary set partitioning combined with binary-input ternary-output (BITO) turbo codes is employed to fully exploit the property of the nonpower- of-two constellation points. Throughout this letter, we focus on an 18-ary HSM with the information rate of 3 bit/symbol as a specific example. It is shown that this system outperforms the standard square 16-QAM with the same rate when PAR is constrained.     

Noncoherent MT-MFSK signals with diversity reception in arbitrarily correlated and unbalanced Nakagami-m fading channels

This paper studies the performance of diversity applied to an efficient modulation/coding scheme using M-ary frequency-shift keying (MFSK) signals, with postdetection noncoherent diversity reception and combining over slow nonselective arbitrarily correlated and unbalanced Nakagami-m fading channels, in which the diversity branches can have unequal signal-to-noise ratios (SNRs), as well as different severity parameter m. This modulation/coding scheme is referred to as multiple tone MFSK (MT-MFSK) and is implemented based on balanced incomplete block design (BIB-design) from combinatorial theory. In MT-MFSK modulation, the number of tones used to represent the signals set is reduced compared with the conventional MFSK modulation, and each MT-MFSK signal is represented by a number of distinct orthogonal tones selected according to BIB-design. This mechanism drastically increase the bandwidth efficiency of the modulated signal and allows the modulator to create implicit frequency diversity. In this paper, we show that by combining the implicit frequency diversity of MT-MFSK signals with the diversity reception introduced by employing multiple receiving antennas, substantial improvements in performance can be obtained. A noncoherent square-law combining (SLC) soft-decision receiver is introduced and a union bound expression for the average symbol error probability is obtained. The effects of arbitrarily values of fading severity parameter m and the arbitrarily correlation between the unbalanced L diversity channels are considered. The system performance is compared with that of the conventional MFSK system. The results show that this modulation/coding scheme creates a multiplicative diversity and, therefore, performs better than the conventional MFSK system in terms of power and bandwidth efficiency.     

An architecture for amplify‐and‐forward cooperative systems with real modulations

This paper proposes a simple architecture for half‐duplex cooperative systems which use amplify‐and‐forward (AF) as a relay strategy and one‐dimensional modulations for source messages. The proposed solution uses the two orthogonal channels of quadrature modulation in order to allow a node to behave simultaneously as a source and a relay. We demonstrate that the new scheme has a similar performance to the conventional orthogonal amplify‐and‐forward protocol without suffering from bandwidth loss, and avoids error propagation problems of previously reported AF superposition schemes. The proposed technique is suitable for applications with low spectral efficiencies and practical adaptive systems where real modulations are implemented based on a quadrature modulation core. Copyright © 2009 John Wiley & Sons, Ltd.     

A Chaotic Interleaving Scheme for the Continuous Phase Modulation Based Single-Carrier Frequency-Domain Equalization System

In this paper, we propose a chaotic interleaving scheme for the continuous phase modulation based single-carrier frequency-domain equalization (CPM-SC-FDE) system. Chaotic interleaving is used in this scheme to generate permuted versions from the sample sequences to be transmitted, with low correlation among their samples, and hence a better bit error rate (BER) performance can be obtained. The proposed CPM-SC-FDE system with chaotic interleaving combines the advantages of the frequency diversity, the low complexity, and the high power efficiency of the CPM-SC-FDE system and the performance improvements due to chaotic interleaving. The BER performance of the CPM-SC-FDE system with and without chaotic interleaving is evaluated by computer simulations. Also, a comparison between the proposed chaotic interleaving and the conventional block interleaving is performed. Simulation results show that, the proposed chaotic interleaving scheme can greatly improve the performance of the CPM-SC-FDE system. Furthermore, the results show that this scheme outperforms the conventional block interleaving scheme in the CPM-SC-FDE system. The results also show that, the proposed CPM-SC-FDE system with chaotic interleaving provides a good trade-off between system performance and bandwidth efficiency.     

Differential modulation and cyclic delay diversity in orthogonal frequency-division multiplex

We propose a new scheme for differential modulation in orthogonal frequency-division multiplexing (OFDM) with cyclic delay diversity. Delay diversity is done in a cyclic manner in order not to exceed the guard interval. However, the increased frequency selectivity, and consequently, reduced coherence bandwidth, causes problems for noncoherent detection of differential modulation in frequency direction. Our proposal is able to cope with the increased frequency selectivity,and enables picking up the spatial diversity in frequency-selective channels with unknown delay spread in combination with standard differential modulation techniques. The new scheme is less complex than differential unitary space-time modulation. The overhead due to reference symbols is minimized and the detection delay is reduced, compared with differential modulation in time direction.     

Intercarrier interference self-cancellation scheme for OFDM mobilecommunication systems

For orthogonal frequency-division multiplexing (OFDM) communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in intercarrier interference (ICI). This paper studies an efficient ICI cancellation method termed ICI self-cancellation scheme. The scheme works in two very simple steps. At the transmitter side, one data symbol is modulated onto a group of adjacent subcarriers with a group of weighting coefficients. The weighting coefficients are designed so that the ICI caused by the channel frequency errors can be minimized. At the receiver side, by linearly combining the received signals on these subcarriers with proposed coefficients, the residual ICI contained in the received signals can then be further reduced. The carrier-to-interference power ratio (CIR) can be increased by 15 and 30 dB when the group size is two or three, respectively, for a channel with a constant frequency offset. Although the redundant modulation causes a reduction in bandwidth efficiency, it can be compensated, for example, by using larger signal alphabet sizes. Simulations show that OFDM systems using the proposed ICI self-cancellation scheme perform much better than standard systems while having the same bandwidth efficiency in multipath mobile radio channels with large Doppler frequencies     

Effects of diversity power control, and bandwidth an the capacityof microcellular CDMA systems

We evaluate the capacity and bandwidth efficiency of microcellular CDMA systems. Power control, multipath diversity system bandwidth, and path loss exponent are seen to have a major impact on the capacity. The CDMA system considered uses convolutional codes, orthogonal signalling, multipath/antenna diversity with noncoherent combining, and fast closed-loop power control on the uplink (portable-to-base) direction. On the downlink (base-to-portable), convolutional codes, BPSK modulation with pilot-signal-assisted coherent reception, and multipath diversity are employed. Both fast and slow power control are considered for the downlink. The capacity of the CDMA system is evaluated in a multicell environment taking into account shadow fading, path loss, fast fading, and closed-loop power control. Fast power control on the downlink increases the capacity significantly. Capacity is also significantly impacted by the path loss exponent. Narrowband CDMA (system bandwidth of 1.25 MHz) requires artificial multipath generation on the downlink to achieve adequate capacity. For smaller path loss exponents, which are more likely in microcellular environments, artificial multipath diversity of an order of as high as 4 may be needed. Wideband CDMA systems (10 MHz bandwidth) achieve greater efficiencies in terms of capacity per MHz     

正交椭圆球面波函数脉冲调制方法

为了提高通信系统的功率效率和频谱效率,该文提出正交椭圆球面波函数(PSWF)脉冲调制方法。该方法利用具有高能量聚集性的椭圆球面波函数作为传输波形来提高通信系统的功率效率,采用时域正交、频谱混叠或交叠的正交脉冲组传输信息,以减小信息传输带宽,提高通信系统的频谱效率。理论分析及仿真结果表明,该方法可使通信系统的单位频带利用率快速接近2 Baud/Hz,且已调信号具有较好的频域能量聚集性,不仅有利于提高系统的功率效率,还可有效减小对相邻通信用户的电磁干扰。     

Comparison of advanced coding and modulation schemes for multicarrier satellite communication systems

Digital satellite communication systems use coherent quaternary PSK (QPSK) as the preferred modulation scheme. In recent years, however, the search for bandwidth and power-efficient digital modulation methods has become an active research area. In this paper the performances of combined coding and modulation schemes employing multilevel signal alphabets are considered, in the framework of a system model which reasonably approximates the INTELSAT SCPC system. The main goal of the research was to investigate whether the efficiency of coded modulation schemes and their savings in transmitted power could be maintained in a system environment dominated by interference more than by the additive white Gaussian noise. A second goal was to compare the performance of signals with constant envelope, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel QAM. In the paper, we propose a channel model which is reasonably close to the real system, and a method for performance evaluation leading to an estimate of the asymptotic power gain of the modulation systems. The channel model and the method are applied to the analysis of coded 16- and 32- PSK and QAM.