A Simple Delay Time Estimation Method and Its Application to Adaptive OFDM Transmissions for Vehicular Wireless Networks

The MIMO transmission against a smart attacker has recently been formulated as a noncollaborative game, in which both the MIMO transmitter and the malicious attacker try to maximize their predefined utilities. In this paper, by carefully analyzing the Nash Equilibrium (NE), we focus on the conditions, in which the gaming results incline to the malicious attacker instead of the MIMO transmitter. In this adverse case, it is highly desirable to develop an effective mechanism to suppress the attack intention by the attacker for better secure communication. Motivated by this, an adaptive secure MIMO transmission scheme was proposed to make the MIMO transmitter better resist malicious attackers in adverse channel conditions. Compared with the existing gaming-based strategy, not only the transmit power of the MIMO transmitter but also the transmission probability will be adjusted in the proposed adaptive secure transmission scheme. Our analysis results show that the proposed scheme can be regarded as a generalized adaptive transmission one, i.e., when the adaptive transmit power policy is enough to suppress the attack motivation, the proposed scheme will be reduced to the adaptive power control scheme; otherwise, both the adaptive transmit power and the adaptive probabilistic transmission can be employed to suppress the attack motivation. The analysis results confirm us that the proposed adaptive transmission scheme provides us a choice to enhance the secure MIMO transmission performance in adverse conditions.

The wide area wireless network (IEEE 802.16 WMAN) supports integrated services such as constant bit rate voice, variable bit rate video, high speed FTP and low speed www data. Efficient resource management in such network is a real challenge because of QoS requirements of integrated services and the error prone nature of the radio channel. In this paper, we mainly focus on the efficient packet transmission mechanism in such network. We propose an efficient channel prediction scheme which combines the handshake probing and prediction together to probe the channel state before transmission. Based on the maximum tolerant BER of different services, channel state is classified into three different states and an adaptive packet transmission scheme for all services under different channel states is introduced. The performance of the proposed schemes are evaluated and the results verified by using extensive simulations.

This paper presents an indoor optical wireless communications using adaptive wireless optical transmission scheme for health monitoring system. Since radio frequency (RF) networks can present electromagnetic disturbances with medical devices, an alternative system based on infrared (IR) technology is studied. In this scheme, optical wireless communication is proposed to transmit the obtained measurements from sensors to a central node and a medical center using intensity modulation-direct detection (IM/DD) with on-off-keying (OOK) modulation. An image sensor is utilized as a receiver, and the signal to noise ratio (SNR) at the image sensor is analyzed with consideration of the half power angle of the optical source, the transmitted power, data rate, and the patient's location. The analytical results indicate that by employing the adaptive transmission scheme, the required SNR of 13.6 dB is achieved.

In recent years, most of the research about distributed video coding focus on how to get the exact side-information and virtual channel estimation parameters in order to achieve better rate-distortion performance. However, there is quite few research about the practical transmission issue, i.e., no practical and effective transmission scheme has been proposed yet for distributed video coding (DVC). Feedback channel based DVC can usually achieve better rate-distortion performance, while leading to long delay because of feed-backs. The traditional video transmission scheme, which doesn't consider the characteristics of DVC, will introduce long delay since the encoder needs to wait until receiving the feedback information. As a result, the effective bandwidth of the network will be reduced greatly. In this paper, we have proposed an adaptive time division multiplexing video transmission scheme for the DVC which can reduce the delay due to waiting feed-backs. Experimental results show that our method can reduce transmission time effectively. And as a result, it can improve the effective bandwidth and the buffer utilization rate, thus higher transmission efficiency can be achieved.

Adaptive transmission schemes are a key part of the radio design for 5G wireless channels. The paper studies the performance of two types of adaptive transmission schemes in cellular downlink. One is based on rateless codes with constant power and the other is fixed-rate codes in conjunction with power adaptation. Using a simple stochastic geometry model for cellular downlink, the focus is to understand the key impact of power adaptation in rateless and fixed- rate coded adaptive transmission. The performance of both rateless and fixed-rate coded adaptive transmission schemes are compared by evaluating the typical user rate and success probability achievable with the two schemes. Based on both theoretical analysis and simulation results, the paper clearly shows that rateless coding simplifies the role of power control in an adaptive transmission scheme.

Multimedia streams impose tight temporal constraints since different kinds of continuous multimedia streams have to be played synchronously. We devise in this paper an adaptive transmission scheme to ensure the continuous and synchronous playback of audio and video streams based on Real-time Transport Protocol. Realization of our adaptive scheme is composed of a series of operations in three stages, namely, (1) dynamic reordering mechanism, (2) decoding-recovery mechanism, and (3) adaptive synchronization mechanism. An empirical study is conducted to provide insights into our adaptive transmission scheme. As validated by our simulation results, the adaptive transmission mechanism is able to strike a good balance of both stable playback and the end-to-end delay reduction. Furthermore, we analyze the jitter resistance, the end-to-end delay, and the buffer size required in order to enhance the applicability of this scheme to more applications that require the transmission of multimedia data.

We investigate the optimal physical-layer secure transmission with artificial noise in the wiretap channel with N antennas at the transmitter, a single antenna at the receiver, and M antennas at the eavesdropper. We analyze the performance and determine the optimal transmission parameters for two distinct schemes: 1) an on-off transmission scheme and 2) an adaptive transmission scheme. For the on-off transmission scheme, where a channel-realization-independent secrecy rate is used for all transmission periods, we derive closed-form expressions for the secure transmission probability, the hybrid outage probability, and the effective secrecy throughput. For the adaptive transmission scheme, where a channel-realization-dependent secrecy rate is used for each transmission period, we derive closed-form expressions for the secure transmission probability, the secrecy outage probability, and the effective secrecy throughput. Using these closed-form expressions, we determine the optimal power allocation between information signals and artificial noise signals for both schemes to maximize the secure transmission probability. We also determine the optimal secrecy rate for both schemes to maximize the effective secrecy throughput. We explicitly examine the impact of N and M on the optimal power allocation and the optimal secrecy rate. Finally, we demonstrate the performance gain of the adaptive transmission scheme over the on-off transmission scheme.

Adaptive transmission in a cooperative network with a half-duplex relay operating in decode-and-forward mode is considered. The main purpose of the paper is maximizing the spectral efficiency of the system, which is reduced by using half-duplex relaying, while the bit error performance is kept below an appropriate threshold. The source transmits its data adaptively using quadratic amplitude modulation. Two adaptive transmission schemes are proposed: the first scheme is named simple adaptive transmission scheme (SATS), and the second one is called high-performance spectral efficiency scheme (HPSES). The SATS has a low complexity system at the destination which does not combine received signals from the source and relay. However, the HPSES uses a linear combination at the destination which is a novel detector to take the possibility of error at the relay into account. Then, we derive exact closed-form expression for the average spectral efficiency and outage probability of the system and an approximate closed-form expression for the average bit error probability. The simulation results corroborates theoretical results. Furthermore, it is shown that despite much lower complexity, the performance of the SATS is close to other well-known schemes. Moreover, the HPSES outperforms other methods of adaptive transmissions in sense of the spectral efficiency and outage probability.

This paper introduces a novel quantitative framework for measuring the risk and the reward provided by adaptive transmission schemes. In particular, the reward is measured as the expected value of the link spectral efficiency in excess of some predefined threshold. The risk, on the other hand, is the nth root of the nth order lower partial moment of the link spectral efficiency distribution. We apply mathematical tools of finance theory to analyze the risk-reward performance of various state-of-the-art adaptive transmission schemes in generic multi- antenna channels. We identify the maximum-return, minimum- risk, efficient, and optimal risk-reward schemes. The numerical results suggest that in a general case the optimal risk-reward scheme is neither the scheme that maximizes the expected link spectral efficiency nor the scheme that minimizes the risk by minimizing, e.g., the outage probability. The financial risk-reward theory brings a new intuition to the understanding of adaptive transmission in nonergodic channels.

An adaptive MIMO transmission scheme using QAM and LDPC code is proposed for an OFDM cellular system employing FDD. By approximating the LLR distribution to a Gaussian distribution, only two parameters, the mean and the normalized standard deviation, are required to be sent to the transmitter, which requires only a few more bits than those required in currently used single carrier cellular systems, such as cdma2000-1x EV-DO. It is shown by computer simulation that the proposed adaptive transmission scheme can provide up to 2/spl sim/3 dB gain over the conventional system using the mean SNR only, at the expense of only 3 more bits in the feedback information.

In this paper, we consider wireless-powered relay network consisting of one source, one wireless powered relay and one sink, where the relay is provisioned with both data buffer and energy storage. Firstly, a novel time-switching transmission scheme is proposed to divide the transmission from source to sink into three phases, namely, the relay energy harvesting phase, the relay receiving phase and the relay forwarding phase. And the achievable end to end (E2E) throughput and optimal timeswitching parameter are derived. Secondly, the transmission scheme is reformulated as a stochastic optimization problem to take into considerations of all the dynamic characteristics of the energy harvesting status, the data buffer status and the underlying time-varying channel conditions. By employing the Lyapunov optimization theory, an online buffer-energy aware adaptive transmission scheme is proposed to adjust the transmission at both source and relay according to the channel state information(CSI), the data buffer state information (BSI) and the energy state information (ESI). Moreover, the tradeoff between the average E2E throughput and the transmission delay is presented to show the great potential of the proposed adaptive transmission design to improve the achievable transmission throughput. Finally, simulations are presented to validate the efficiency of the proposed relaying protocols.

Ultra-reliable low-latency communication (URLLC) is one of the service categories envisioned by fifth-generation (5G) wireless systems for supporting mission-critical applications. These applications require the transmission of short-length data packets with a high level of reliability and hard latency bound. Achieving targeted reliability in URLLC is challenging because of dynamic channel conditions and network load. Therefore, retransmission of lost data packets is essential for increasing the reliability of data. Again, an optimized radio resource allocation for these (re)transmission schemes is required to satisfy URLLC constraints. Hence, we propose a reinforcement learning-based resource allocation for adaptive transmission and retransmission scheme. We demonstrate the use of machine learning in optimizing the resource usage under variable network load conditions.

In this paper, an adaptive cooperative transmission scheme according to the user location is proposed. The proposed cooperative scheme considers the destination user location and applies cooperative scheme properly. If the destination user is located in the cell boundary, the quality of communication is degraded in the broadcasting system. In the conventional scheme, broadcasting base station and cellular base station are used to obtain high performance. However, the quality of communication is not well guaranteed and the transmission distance is increased since the destination user is far from each base station. Therefore, the adaptive transmission scheme for the user location is proposed. In the simulation results, the proposed scheme can obtain more improved performance than the conventional scheme.

We propose in this paper a practical adaptive modulation and channel encoding scheme for spatial multiplexing multiple-input multiple-output (MIMO) systems. The proposed scheme aims not only to maximize the average spectral efficiency (ASE) for a given bit error rate (BER) constraint but also to lower the computational and hardware complexity. First, an adaptive transmission principle for spatial multiplexing MIMO systems is presented under the assumption that the channel state information (CSI) is available at the receiver; Furthermore, we propose not only an adaptive modulation scheme for different transmit antennas but also an adaptive scheme which combines channel encoding and modulation. Finally we demonstrate from the simulation that the proposed scheme is of practical significance since it provides a well-behaved tradeoff between the ASE and complexity in comparison with the singular value decomposition (SVD) based adaptive transmission scheme with the optimal ASE performance and high computational complexity.

We propose an orthogonal frequency division multiplexing frequency division multiple access (OFDMA) system with an adaptive multiple antenna transmission scheme for future wireless communication systems. In the system, both a transmit diversity scheme with high order modulation and a spatial multiplexing scheme with low order modulation are employed for the given spectral efficiency, between which the proper transmission scheme is selected according to the channel state. It is observed that the proposed system with a selection algorithm based on the post processing SNR reduce the average transmit power.