With the growing demand of serviceability for mobile terminals, mobile terminals are facing the problem of coexistence of multiple standards, functions and systems [1]. If traditional terminals are upgraded in the pattern of hardware upgrade to implement upgrading and capability enhancement, a large amount of electronic waste will be generated [2]. Therefore, it is necessary to break through the high-performance, open and reconfigurable software-defined radio (SDR) method of communication and perception. Faced the above problems, this paper proposes a generalized computational complexity analysis model, which gives a modular computational complexity analysis method by decoupling and separating the functions of the communication system.

A power amplifier(PA) is inherently nonlinear device and is used in a communication system widely. Due to the nonlinearity of PA, the communication system is hard to work well. Digital predistortion (DPD) is the way to solve this problem. Using Volterra function to fit the PA is what most DPD solutions do. However, when it comes to wideband signal, there is a deduction on the performance of the Volterra function. In this paper, we replace the Volterra function with B-spline function which performs better on fitting PA at wideband signal. And the other benefit is that the orthogonality of coding matrix$A$could be improved, enhancing the stability of computation. Additionally, we use compressive sampling to reduce the complexity of the function model.

Massive multiple-input-multiple-output (MIMO) has been considered as one of the promising technologies for the future communications due to its high spectrum efficiency. In massive MIMO systems, hybrid precoding is widely adopted for it can reduce the unacceptable power consumption with a small number of radio- frequency (RF) chains. However, one RF chain can serve at most one user. Consequently, the number of simultaneously served users are strictly limited. To break this limitation, the idea of beamforming MIMO non-orthogonal multiple access (NOMA) has been proposed. In beamforming MIMO NOMA systems, one RF chain can support two or more users, where users with the same beam selection are paired into one cluster and served by an identical RF chain. However, the traditional beams are so narrow that only a few users can find a match while most of the users still remain single and perform orthogonal multiple access. To solve the problem, we propose a new scheme called multi-resolution beamforming and user clustering scheme. We first utilize beams with narrow angle range and higher array gain for user clustering. Those users which cannot be paired with these beams are clustered by a new beam codebook whose beams have a wider angle range. The selected wide beams are well-designed to avoid bringing interference to the previously paired users. The proposed scheme raises the possibility for users being paired into clusters while keeping a satisfying array gain. Therefore, more users in the cell can take advantages of NOMA to achieve a higher spectral efficiency. The simulation results demonstrate that the proposed scheme outperforms existing schemes under different scenarios.

As the bandwidth resource in TV white space (TVWS) is permitted to be used for the secondary users, multiple secondary networks coexisting in the same geographical area can provide multiple services without interfering with the primary service, such as the TV broadcasting. To satisfy the minimum rate requirements and maximise the sum rate of the multiple services, the problem of resource allocation can be modelled as a mixed integer non‐linear programming (MINLP). According to this model, the joint bandwidth and power allocation (JBPA) method is proposed to solve the resource allocation for multiple services. The JBPA method is sub‐optimal, which can approximate the performance of the optimal two‐step exhaustive search (TSES) method very well, especially when the number of services is larger than the number of idle channels. Compared with TSES, the JBPA method decreases the complexity from exponential level to polynomial level. Besides, compared with one channel occupied by single service, the JBPA can serve more services and provide stable performance when the number of services varies dynamically. Compared with the algorithm random bandwidth allocation, the JBPA can approximate the optimal performance provided by TSES better with the time complexity of the same order.

In spatial modulation (SM) systems, the distribution of amplitude-phase modulation (APM) symbol causes the tradeoff of detection performance between APM symbol and active antenna, which infers the overall capacity of SM system. In this paper, the APM constellation and symbol labeling of SM system is investigated. The optimized APM constellation is designed to maximize the system coded modulation average mutual information (CM-AMI). The symbol labeling of SM system is optimized with binary switching algorithm (BSA) using the symbol detection pairwise error probability (PEP) criteria. Moreover, the proposed APM constellation and symbol labeling are applied in a coded spatial modulation (SM) system with the bit-interleaved coded modulation and iterative demapping (BICM-ID). Simulation result shows the BICM-ID SM system with proposed constellation and symbol labeling has a signal-to-noise ratio (SNR) gain compared to conventional constellation system and independent demapping system.

Combined with client pairing on nonorthogonal multiple access (CP-NOMA), carrier sense multiple access/collision avoidance (CSMA/CA) can provide more connectivity for clients in downlink phase and alleviate the low transmission efficiency from rate anomaly problem. Compared with conventional CSMA/CA system, the proposed enhanced CSMA/CA with CP-NOMA can save about half of the time cost to send signaling overhead and provide improvement in the efficiency of data transmission. Similar to saturated throughput, the long-term average rate is defined and used to illustrate the performance of the proposed method. Considering the criterion of the fairness and the received signal to noise ratio (SNR), the selection of client pairing in NOMA could be optimized to maximize the data transmission rate in NOMA. Providing the channel access for more clients, the efficiency of the downlink transmission is enhanced in the proposed scheme. In the application of Internet of Things (IoT), The enabling technology supporting more clients in connectivity really makes a big difference. Besides, the enhanced CSMA/CA with CP-NOMA is compatible with conventional CSMA/CA system.

LDS-OFDM and SCMA are two examples of non orthogonal multiple access (NOMA), which is considered to be a promising technology for next generation wireless communications due to its larger capacity region compared with orthogonal multiple access (OMA). Iterative receiver structure is used in these two systems to get better performance than the noniterative receiver, but a direct implementation of iterative receiver with conventional message passing algorithm has a prohibitive computational complexity, especially when the system uses high order modulation. In this paper, Gaussian approximation is used to solve this problem, and can reduce the complexity of detector effectively. Simulation results demonstrate that the proposed Gaussian approximation based iterative receiver offers significant performance gains over the traditional non-iterative receiver structure. Even compared with the computationally intractable message passing based iterative receiver, the performance does not degrade much. This means that the proposed method offers a tradeoff between performance and complexity, and is a good candidate for future use in LDS-OFDM and SCMA systems.

Compared with Wireless Local Area Networks (WLANs) in the ISM band, smaller path loss of the spectrum in TV White Space (TVWS) provides larger coverage region with the same power budget. More nodes derived from the larger coverage region increase the collision probability, which damages the throughput efficiency of carrier sense multiple access#x002F;collision avoidance (CSMA#x002F;CA) protocol in 802.11af. The scheme of the Channel Access based on Frequency Contention (CAFC) exploits single sub-carrier of Filtered Bank Multi-Carrier (FBMC) to realize frequency contention. CAFC improves the system throughput efficiency by decreasing the collision probability and removing channel idle time. The set of possible frequency contention outcomes can be enlarged to further decrease the collision probability with little cost appended to the system complexity. Compared with conventional CSMA#x002F;CA in 802.11af, the simulation indicates that the CAFC scheme enhances the saturated throughput efficiency significantly. Besides, the CAFC scheme is designed to be compatible with 802.11af, which reduces the application cost in practice.

Generalized spatial modulation (GSM) is an extended architecture to the spatial modulation multiple antenna system. The GSM system uses multiple activated transmit antennas to further exploit the system transmission capacity. In this paper, we consider the GSM systems with channel diagonalization (CD-) transmitter pre-coder (TPC), channel inversion TPC, and without TPC. For each TPC scheme, the pairwise activated antenna detection discriminant and closed-form antenna detection pairwise error probability (PEP) of the GSM system are derived. We use the antenna detection PEP to calculate the analytical antenna detection symbol error rate union bound and the mutual information lower bound. We use asymptotic methods to analyze antenna detection diversity and coding gains of GSM system with or without TPC when the signal-to-noise ratio is high. Together with complexity analysis on the pre-coders and antenna detectors, we discover the CD-TPC trades the antenna detection performance for complexity reduction, while the CD-TPC scheme achieves a balance between the performance and complexity. This paper introduces methods to the performance evaluation of the GSM system, and provides a guideline for the GSM system design such as antenna configuration and TPC schemes selection.

Generalized spatial modulation (GSM) is an extended architecture to the spatial modulation (SM) multiple antenna system. Multiple activated transmit antennas (TAs) are applied in the GSM system to further exploit the system transmission capacity. In this paper, we consider the transmitter pre-coding (TPC) GSM systems with channel diagonalization (CD) and channel inversion (CI) pre-coding schemes. The pairwise activated TA detection discriminant and closed-form pairwise error probability (PEP) function are derived. We use the TA detection PEP to calculate the analytical TA detection symbol error rate (SER) union bound and the mutual information lower bound. The analytical results are verified by numerical simulation over Rayleigh fading channels. We investigate the system with different number of antennas and TPC schemes to evaluate the error probability and mutual information performance of the GSM system. The results show that the CD-TPC GSM system with equal power allocation has the most TA detection mutual information, and the CD-TPC system with water-filling power allocation has the most joint APM domain and space domain mutual information.

Spatial modulation (SM) is a recently proposed multiple-input multiple-output (MIMO) architecture that exploits the space domain for information transmission. In this paper, SM systems with continuous amplitude-phase modulation (APM) and the corresponding maximum likelihood (ML) active transmit antenna detector are considered. We introduced a method to compute the theoretical transition probability matrix and the mutual information of the ML antenna detector. For SM multiple-input single-output (MISO) system, we derive the error probability and the mutual information of the antenna detector in closed-form. For multiple receive antenna SM system, the union bound of error probability and the lower bound of antenna detection mutual information are proposed. The analytical results are verified by numerical simulation over Rayleigh fading channels. We investigate systems with different number of antennas and APM symbol input distributions to evaluate the performance of SM. The joint APM and antenna detection mutual information of SM systems is compared to the capacity of vertical Bell Labs layered space-time (V-BLAST) spatial multiplexing MIMO scheme. Our research gives achievable transmission rates of SM-MISO/MIMO systems and can be a guideline for suitable application scenarios.

An error transfer chart is introduced to trace the iterative process of the decision feedback equalizer for the single-carrier modulation. In the investigated iterative MF-DFE structure, the forward filter is set to the matched filter to maximize the signal power, while the feedback filter is used to cancel the inter-symbol interference. MMSE detection is applied to minimize the decision error power. The trajectory of iterations is shown in the error transfer chart, in which MF-DFE maps a decision error power to an SINR and MMSE detection further converts the SINR to a new decision error power. The final state of iterations is shown to be the intersection of the MMSE curve and error power transfer curve corresponding to the MF-DFE algorithm. It is shown by simulation that the error transfer chart is a useful tool to analyze the convergence of non-linear iterative equalizers.

Frequency domain equalization (FDE), as a linear equalizing method, is widely adopted in many applications with either OFDM or single carrier (SC) modulation. This paper analyzes the the noise transfer effect, a case for noise colorization, after FDE. This process is investigated for CP-OFDM, ZP-OFDM and SC systems where SC is treated as a multi-carrier modulation with the number of subcarriers equal to 1. Based on this analysis and by assuming the de-mapping independence among subcarriers, the average channel capacity for the systems is derived. We have proved that the capacity of the CP-OFDM system is at least equal to that of ZP-OFDM in both low and high SNR scenarios and that the capacity of the SC system is no greater than that of either ZP-OFDM or CP-OFDM systems. In a multi-path channel, if the IDFT size of the OFDM symbol is not equal to the DFT size of the equalizer, the leakage of the enhanced noise in a deeply faded sub-channel will cause the loss of capacity in adjacent sub-channels and the overall average capacity is thus reduced.

This paper presents a decision directed frequency and clock tracking scheme to improve the spectrum efficiency of burst mode OFDM transmission with frequency selective channel. OFDM divides one broadband channel to parallel narrowband subchannels of different channel characteristics. In this scheme, the subcarriers with better attenuation are selected out to do the decision-directed based clock and frequency tracking. a novel phase error detection method is proposed which keeps the hard decision working well when tracking is performed. Furthermore, Particular algorithm is designed to ensure the carrier frequency offset and sampling frequency offset could be solved out from detected phase error. Simulations illustrate that the new scheme can work well in typical system.

Time domain synchronous OFDM (TDS-OFDM) has higher spectral efficiency than cyclic prefix OFDM (CP-OFDM), but suffers from severe performance loss over fast fading channels. In this paper, a novel transmission scheme called time-frequency training OFDM (TFT-OFDM) is proposed. The time-frequency joint channel estimation for TFT-OFDM utilizes the time-domain training sequence without interference cancellation to merely acquire the time delay profile of the channel, while the path coefficients are estimated by using the frequency-domain group pilots. The redundant group pilots only occupy about 1% of the useful subcarriers, thus TFT-OFDM still has much higher spectral efficiency than CP-OFDM by about 10%. Simulation results also demonstrate that TFT-OFDM outperforms CP-OFDM and TDS-OFDM over time-varying channels.

To reduce the complexity of existing transmit diversity solutions for time domain synchronous OFDM (TDS-OFDM), a simple transmit diversity scheme is proposed in this paper. The space shifted constant amplitude zero autocorrelation (CAZAC) sequence is used for time-domain channel estimation. Two types of flexible frame structures are investigated for cyclicity reconstruction of the received inverse discrete Fourier transform (IDFT) block. Regarding to channel estimation and cyclicity reconstruction, the complexity of the proposed scheme is only about 7% of the conventional solutions. With the penalty of small loss in spectral efficiency, the proposed scheme achieves better bit error rate performance over doubly selective channels, which is demonstrated by the simulation results.

The existing transmit diversity schemes for time domain synchronous OFDM (TDS-OFDM) is only suitable either for fast time-varying but weakly frequency-selective channels, or strongly frequency-selective but slow fading channels. In this paper, the space-time shifted constant amplitude zero autocorrelation (CAZAC) sequence based TDS-OFDM transmit diversity scheme is proposed for doubly selective channels. The spaceshifted CAZAC sequence is used for channel estimation, and the time-shifted sequence is utilized for the cyclicity reconstruction of the received inverse discrete Fourier transform (IDFT) block. Compared with the state-of-the-art solutions, the proposed scheme has lower complexity irrelative to the transmit antenna number, and it achieves better bit error rate (BER) performance under various multi-path fading channels.

Time domain synchronous OFDM (TDS-OFDM) with higher spectral efficiency than cyclic prefix OFDM (CP-OFDM)was originally proposed for downlink broadcasting transmission. To support multi-user uplink scenarios, this paper proposes a novel multiple access scheme called time domain synchronous frequency division multiple access (TDS-FDMA), wherein an uniform frame structure and its corresponding receiver algorithms are presented for both single-carrier and multicarrier signal transmission. Compared with typical OFDMA systems, TDS-FDMA has higher spectral efficiency. The multi-user TDS-FDMA receiver has lower complexity than the conventional single-user TDS-OFDM receiver, and it can achieve better bit error rate (BER) performance under the slow to medium time-varying channels.

Compared with the global positioning system (GPS), the digital television (DTV) broadcasting signal is a promising candidate for position location due to low implementation cost and strong signal reception. Without changing the current infrastructure of the Chinese DTV broadcasting network, this paper proposes a novel positioning scheme using the multi-carrier pseudo-noise (PN-MC) training sequence in the guard interval of the time domain synchronous OFDM (TDS-OFDM) signal frame. Different from the existing positioning methods based on timing synchronization or super resolution algorithms, the joint time-frequency estimation utilizing the properties of the received PN-MC sequence both in the time and frequency domain with respect to transmission delay, results in the accurate time of arrival (TOA) estimation. Performance of the proposed scheme is evaluated by Monte Carlo simulations in comparison with other the-state-of-art methods. The positioning accuracy of less than 0.1 m when the signal-to-noise ratio (SNR) is greater than 15 dB is achieved, under both the additive white Gaussian noise (AWGN) and the simulated multi-path channels.

The unavoidable Doppler frequency shift reduces the correlation peak for code acquisition in global positioning system (GPS). In contrast to conventional methods where the code phase and Doppler frequency shift are separately treated, this paper proposes a novel three-step scheme for joint code acquisition and Doppler estimation, whereby not only the Doppler effect on the correlation peak is removed, but also the reduced detection probability due to noise enhancement in low signal-to-noise ratio (SNR) environments is avoided. The theoretical analysis shows that the proposed method has low complexity and fast acquisition speed. Computer simulations demonstrate that code acquisition with high detection probability and Doppler frequency shift estimation with high accuracy can be simultaneously achieved.

To improve the system capacity of conventional orthogonal frequency division multiplexing (OFDM) systems, the layered modulation OFDM scheme is proposed. The modulated OFDM symbols are separated into two layers as differential modulated symbols and coherent symbols. The differential symbols are used as pilots, which are combined with the coherent modulated data and sent out by the transmitter. At the receiver side, the data in pilot position will be recovered after the differential demodulation. The recovered differential symbols will be used for channel estimation to demodulate the coherent symbols. Furthermore, the differential modulated data can employ low reception threshold and low complexity demodulator, which will facilitate the usage in mobile TV transmission. Simulations show the two layers' reception can be compatible with each other.

This paper summarizes some key features for future Chinese digital television terrestrial broadcasting (DTTB) systems including improved frame structure, transmit diversity, advanced channel coding and modulation, multi-service support, broadcasting return channel solution and etc.

Time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) outperforms cyclic prefixed-OFDM (CP-OFDM) in spectrum efficiency at the expense of higher complexity. Up to now, TDS-OFDM has only been used in unidirectional transmission, such as broadcasting applications. The overwhelming complexity of removing the implicitly superposed interferences between the PN sequences and IDFT information blocks, caused by multiple users, hinders the application of time-domain synchronous orthogonal frequency division multiple access (TDS-OFDMA) in multi-user communication scenarios. To solve this problem, this paper proposes a novel TDS-OFDMA scheme, including joint cyclicity reconstruction and joint channel estimation, utilizing the new "time-space two-dimensional frame structure". Theoretical analysis and computer simulation show that the proposed scheme not only can achieve the purpose of multiple access but also has an even better system performance in mobile environment than the conventional single-user TDS-OFDM system.

In order to improve the system performance over wireless fading channel, transmit diversity technique has been proven as an attractive and effective solution especially for broadcasting systems. In this paper, a PN sequence design scheme based on both cyclic-shift m-sequences and space-time block coded (STBC) m-sequences for time domain synchronous orthogonal frequency-division multiplexing (TDS-OFDM) system with transmit diversity is proposed. Based on this novel design, flexible channel estimation which provides a trade-off between maximum delay spread and maximum Doppler spread over double-selective channel is investigated and a radix-2 fast Fourier transform (FFT) approach is adopted for implementation from the viewpoint of computational complexity. Simulations show that the performance of the proposed transmit diversity scheme is better than conventional one and perform well under different propagation conditions.

As one of the most common linearization techniques, adaptive digital predistortion minimizes the difference between the input signal of the predistorter and the feedback signal from the power amplifier. The loop delay between these two signals must be controlled precisely so that the convergence of the predistorter should be assured. In this paper a novel two-stage loop delay correction scheme is presented. In the first stage, the integer delay between the input signal and the feedback signal is estimated based on the cross-correlation of them. In the second stage, the fractional delay between these two signals are corrected by a delay lock loop (DLL) circuit, in which a novel timing error detector used as the discriminator is proposed. The proposed loop delay correction scheme is applied to an adaptive digital predistorter in an orthogonal frequency-division multiplexing (OFDM) system. Simulation results show that the proposed loop delay correction method eliminates the loop delay perfectly, so that nearly optimal power spectral density (PSD) performance is achieved and a high degree of linearization is realized.

The implementation of OFDM system suffers from the effect of phase noise generated by local oscillator (LO), which disturbs the orthogonality between subcarriers and causes intercarrier interference (ICI). In this paper, the symmetric conjugate-negative property of the ICI weighting function is found. Based on that, the ICI self-cancellation of symmetric data-conjugate method is studied to suppress phase noise. The carrier-to-interference ratio (CIR) improvement by this method is shown to be larger than 22 dB in flat fading channel. For a BER of 10-3, this method can tolerate a phase noise standard deviation of 7 deg in flat fading channel. Moreover, this method could offer frequency diversity gain in frequency selective channels. Both analytical and numerical results show that this method outperforms the conventional schemes

This paper describes a novel code acquisition and symbol timing recovery method for time domain synchronous OFDM (TDS-OFDM). It is based on the correlation peak of the PN sequence in the frame sync, in this way it is possible to decrease the influence from noise or interference. It is derived in the AWGN channel, but simulations show that it can also perform well in multipath channels.