Performance of efficient tactical UHF-satcom waveforms: occupied bandwidth, coding gain, spectral efficiency, bit error rate, and adjacent channel interference

Multicarrier transmission techniques like multicarrier code division multiple access (MC-CDMA) is the strongest contender for the future generation wireless networks which is supposed to cater to the need of very high data rate with mobility and at the same time combat multipath and intersymbol interference in a spectrally efficient manner. To enhance the spectral efficiency further, some form of adaptive modulation is being proposed (Wasantha et al. (2002)). In this paper, first of all, we simulate the performance of various single-h continuous phase modulation (CPM) schemes in an MC-CDMA system by varying the two CPM parameters - size of symbol alphabet (M) and modulation index (h). The parameter sets considered are {M=2, h=0.5}, {M=2, h=0.875}, {M=4, h=0.5} and {M=4, h=0.875}. Simulation results show that the higher order modulation schemes (M=4) need better channel conditions than the lower order schemes (M=2) for a given bit error rate (BER). Moreover, as expected (Xiong (2000)), h=0.875 (approximate optimum value) gives a better BER performance than h=0.5 for a given BER. Based on these simulation results, we then design two adaptive modulation based systems, one considering h=0.5 and the other with h=0.875, each with M=2 and 4. Results of the adaptive systems clearly indicate that the adaptive switching of the modulation formats in each of these two systems increases the system capacity per given bandwidth (spectrum efficiency) effectively without sacrificing the expected BER performance. Also, it is seen that the adaptive system with h=0.875 is superior to the h=0. 5 system, both in terms of BER performance and the number of simultaneous users, but obviously at the cost of reduced bandwidth efficiency as higher the value of h, the higher bandwidth it requires.

Continuous phase modulation (CPM) and trellis-coded modulation are well-understood schemes that layer trellis codes with multilevel modulation to produce efficient bandwidth waveforms. This paper describes a novel modulation scheme which takes advantage of existing trellis codes and adds parallel branches to create a new modulation with greater spectral efficiency and reduced receiver complexity. The first part of the paper discusses the trade-off between Euclidean distance and modulation bandwidth for the standard 1-REC CPM waveform. A set of orthogonal signals can be added to the CPM constellation which provides a series of parallel branches in the natural trellis structure of the CPM modulation. The corresponding bandwidth expansion and throughput improvement is analyzed and the advantages of this modulation technique are discussed. This new, non-constant envelope CPM waveform is compared to the multi-level, multi-amplitude CPM waveform (described in Proakis). In similar fashion, a trellis-coded, shaped PSK modulation is expanded to include orthogonal signal shaping and the power and spectral efficiencies are discussed.

In order to understand the optimal parameter settings of spectrally efficient continuous phase modulation (CPM), we elaborate on our previous work on numerically optimized CPM. An empirical model is developed based on an expression for the effective bandwidth of CPM, an approximate expression for the smallest Euclidean distances of spectrally efficient CPM and observed properties of the numerically optimized phase pulses. We find that the optimized phase pulses, which resulted from a joint optimization of modulation index and phase pulse, share common properties for different alphabet sizes and different spectral efficiencies. These properties are described by three phase pulse parameters, and we show that they attain approximately equal values at the so-called saturation length. The model can predict the minimum Euclidean distance at the saturation length for a CPM system using an even-integer alphabet and jointly optimized modulation index and phase pulse, and it partly extends to less spectrally efficient CPM systems.

Continuous phase modulation (CPM) is known for its attractive spectral properties. Furthermore, CPM has the property that the modulation signal maintains a constant envelope, so CPM is effective for satellite communications. Recently, generalized nonlinear CPM (GNCPM), which can achieve a larger minimum Euclidean distance than ordinary CPM, was introduced. In this paper, we propose a convolutional coded GNCPM to improve the bit error rate (BER) performance of uncoded GNCPM without expanding bandwidth. Combination CPM with convolutional coding causes an increased number of phase trajectory patterns which can cause the bandwidth expansion. Therefore, in our proposed model, to control the bandwidth, we pay attention to the phase trajectory pattern which is already owned by uncoded GNCPM and change the modulation index appropriately, depending on the input symbols, to keep the number of phase trajectory patterns the same as in uncoded GNCPM. First, we consider the most suitable assignment of the modulation index which can increase the Euclidean distances without bandwidth expansion. Next, we theoretically derive the upper bound on the error event probability of the proposed model in additive white Gaussian noise (AWGN). The performance of the proposed convolutional GNCPM, obtained by computer simulation, shows that the proposed model can improve BER performance without bandwidth expansion. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(8): 42–50, 1998

In this paper author demonstrates the relationship between spectral efficiency and energy efficiency for 10 Gbps, 40 Gbps and 100 Gbps transmission systems with NRZ-OOK, NRZ-DPSK and DP-QPSK modulation formats respectively. The focus of this research is the wavelength division multiplexed (WDM) transmission systems with Forward Error Correction (FEC) technology with required Bit Error Rate (BER) level that does not exceed 10−3. For this purpose the signal BER level versus cross-channel interval response is evaluated. Obtained data was used for the regeneration length calculations with purpose to define the number of regeneration steps for 200km and 2600km transmission systems. In order to observe relationship between spectral and energy efficiency, power consumption was calculated using different crosschannel intervals −37.5 GHz, 50 GHz and 100 GHz, by means of what different spectral efficiencies were reached. The total power consumption of transmission system was calculated by defining the quantity and power consumption values for all WDM system elements that require electrical energy. In this paper author demonstrates how the amount of transmitted information influence the total system power consumption in each considered transmission system and by using obtained data and spectral efficiency data, the systems energy efficiencies were calculated.

Continuous phase modulation (CPM) has been widely used in telecommunication and aeronautical telemetry system due to its high power and spectral efficiency. Non-coherent detection is a kind of feasible CPM detection method if there is large phase noise or residual carrier frequency offset. Near-optimal non-coherent sequence detection, which is based on Viterbi algorithm, has a performance close to that of maximum-likelihood sequence detection (MLSD). However, near-optimal non-coherent detection of CPM is very complicated to be implemented, and it is even more difficult to achieve a high speed due to feedback in the process of calculating branch metrics, add-compare-select (ACS), updating the beginning phase and phase reference symbol. In this paper, we first review near-optimal non-coherent detection of CPM, and then we present a high speed design of FPGA implementation for near-optimal non-coherent detection of a 64 state, 4-ary, length-3T raised cosine (3RC) CPM on Xilinx XC7VX690T device. In our scheme, the frequency pulse truncation is used to simplify the CPM detection. We propose a feedback processing in parallel for different states of CPM trellis to achieve a low latency. Furthermore, we develop a recursive implementation architecture for the process of updating the beginning phase. We achieve the CPM bit rate of 25Mbps for the on-chip processing clock of 100MHz. The results of simulation shows near-optimal non-coherent detection performs much better the coherent detection when residual carrier frequency offset or phase noise exists. It is found that the implementation can achieve a degradation in the Eb/N0 from computer simulation of as small as 0.3 dB for an average BER=10-5.

In this letter, motivated by the superiority of continuous phase modulation (CPM) signals, a binary CPM with modulation index 0.5 is considered into downlink symbol- asynchronous non-orthogonal multiple access (ANOMA) to enhance power and spectral efficiency, especially for resource-limited wireless communications. According to the maximum likelihood (ML) criterion, a Viterbi-based block-by-block detector (VB-BBD) is first proposed. Considering the asymptotics of Toeplitz matrices, a DFT matrix diagonalization-based symbol-by-symbol detector (DFTD-SSD) is also given. Finally, the detection complexity analysis is provided. Numerical results reveal the optimal time offsets with different modulation formats for a two-user system, and show that time asynchrony can bring about 3dB and 6dB performance gains at a bit error rate (BER) of 10−4. The relationship between BER performance and different power levels, frequency pulses, response lengths is also investigated.

In this paper, 4 × 4 multiple-input multiple-output (MIMO) radio over 7-core fiber system based on sparse code multiple access (SCMA) and OFDM/OQAM techniques is proposed. No cyclic prefix (CP) is required by properly designing the prototype filters in OFDM/OQAM modulator, and non-orthogonally overlaid codewords by using SCMA is help to serve more users simultaneously under the condition of using equal number of time and frequency resources compared with OFDMA, resulting in the increase of spectral efficiency (SE) and system capacity. In our experiment, 11.04 Gb/s 4 × 4 MIMO SCMA-OFDM/OQAM signal is successfully transmitted over 20 km 7-core fiber and 0.4 m air distance in both uplink and downlink. As a comparison, 6.681 Gb/s traditional MIMO-OFDM signal with the same occupied bandwidth has been evaluated for both uplink and downlink transmission. The experimental results show that SE could be increased by 65.2% with no bit error rate (BER) performance degradation compared with the traditional MIMO-OFDM technique.

The paper considers a wireless transmission system in a multiple-user environment. It involves a combination of non-binary convolutional codes with Continuous-Phase Modulation (CPM) for transmission in an uplink channel using the Frequency Division Multiple Access (FDMA) method. For a more efficient available band utilization, the distances between individual system user carriers are decreased. In order to reduce the bit error rate (BER) a concatenation of CPM with convolutional codes over a ring has been used and a low-complexity iterative algorithm for inter-carrier interference (ICI) cancellation was employed on the receiver side. BER results obtained in computer simulations are presented for the proposed solution.

Power Amplifier (PA) is a very important component in communication systems which consume a significant fraction of the total energy and is mostly nonlinear. There is an inverse relationship between the PA efficiency and its linearity. Nonlinear PAs are desirable from an efficiency point of view. The price paid for higher efficiency is that it causes growth in spectrum and causes adjacent channel interference. It also causes in-band distortion, which degrades the bit error rate (BER) performance. Transmission systems, like orthogonal frequency-division multiplexing (OFDM), has tolerance to inter-symbol interference and good spectral efficiency but are subjected to nonlinearities of power amplifiers, due to their high peak-to-average power ratio (PAPR), which occurs because of large fluctuations in their signal envelopes. To reduce the spectral regrowth and to reduce BER, PA linearization is necessary. In this paper, Peak clipping, random phase shifting, selected mapping (SLM) and dummy sequence insertion (DSI) methods have been presented to reduce the PAPR and consequently the effect of nonlinearity and to improve the spectral and energy efficiency of PA.

Recent wireless communications systems have adopted orthogonal frequency-division multiplexing (OFDM) due to its robustness against fading channels with simple receiver structure. However, it results in poor power amplifier (PA) efficiency or otherwise suffers from severe nonlinear distortion that causes adjacent channel interference (ACI) because of its high peak-to-average power ratio (PAPR) property of transmit signals. To mitigate this issue, DFT-precoded OFDM has been adopted in the LTE-A standard, which virtually forms single-carrier signals and thus generates lower PAPR than the original OFDM. Nevertheless, as the information rate increases for better spectral efficiency, the performance of DFT-precoded OFDM with simple linear detection becomes inferior to that of the original OFDM over frequency-selective fading channels when both the systems are protected by high-rate channel coding. In this work, we propose an adaptive use of DFT-precoding for OFDM where the DFT operation is applied only when the generated OFDM symbol has large dynamic range and thus causes severe nonlinear in-band distortion after clipping and filtering. It is shown that a good trade-off in terms of bit error rate (BER) performance can be achieved while maintaining the specified level of the PA efficiency and the amount of out-of-band radiation.

The attractive properties of the digital constant amplitude modulation scheme CPM (continuous phase modulation) have been demonstrated in a previous paper in this journal.1 This concerned both the power and spectral efficiency of the large family of CPM schemes over the Gaussian channel.In this paper the considered channel can be both bandlimited or band‐ and amplitude‐limited at the same time. Analytical results as well as simulations are presented for a number of selected CPM schemes.In today's increasing demand for bandwidth, CPM is an attractive candidate for future satellite applications because of its spectral efficiency. In addition to this comes the fact that the transmitted signal has a constant amplitude and good detection performance when optimal coherent detection is performed.

The effects on the performance of differentially detected Gaussian minimum shift keying (GMSK) signals operated in the presence of adjacent channel interference (ACI), modulator impairments, amplifier nonlinearities and additive white Gaussian noise (AWGN) is investigated. By means of computer simulation, the bit error rate (BER) performance of 1- and 2-bit conventional and decision feedback differentially detected (C-DD and DF-DD) GMSK systems in the presence of static and Rayleigh faded ACI is obtained. It is found that the best performance is achieved by the 2-bit DF-DD receiver and has resulted in BER performance improvements for the static ACI channel and error floor reductions for the Rayleigh faded ACI channel.

The effects on the performance of differentially detected Gaussian minimum shift keying (GMSK) signals operated in the presence of adjacent channel interference (ACI), modulator impairments, amplifier nonlinearities and additive white Gaussian noise (AWGN) is investigated. By means of computer simulation, the bit error rate (BER) performance of 1- and 2-bit conventional and decision feedback differentially detected (C-DD and DF-DD) GMSK systems in the presence of static and Rayleigh faded ACI is obtained. It is found that the best performance is achieved by the 2-bit DF-DD receiver and has resulted in BER performance improvements for the static ACI channel and error floor reductions for the Rayleigh faded ACI channel.

Continuous phase modulation (CPM) with 1-bit quantization at the receiver is promising in terms of energy and spectral efficiency. In this study, CPM waveforms with symbol durations significantly shorter than the inverse of the signal bandwidth are proposed, termed faster-than-Nyquist CPM. This configuration provides a better steering of zero-crossings as compared to conventional CPM. Numerical results confirm a superior performance in terms of BER in comparison with state-of-the-art methods, while having the same spectral efficiency and a lower oversampling factor. Moreover, the new waveform can be detected with low-complexity, which yields almost the same performance as using the BCJR algorithm.