Reverse Link Research Articles

Enhanced cooperative communication MAC for mobile wireless networks

In this paper, we propose a new MAC (medium access control) protocol called enhanced cooperative communication MAC (ECCMAC) based on IEEE 802.11. The major objective of ECCMAC is to maximize the benefits of cooperative communication. We first propose a scheme for selecting and maintaining the best relay node. Second, since both cooperative communication and network coding rely on the selection of a relay node, we consider exploiting a network coding technique for additional throughput improvement. Third, to accommodate asymmetric link rates between a sender and a relay node, we employ ECCMAC to measure forward and reverse link rates, whereas prior works have simply assumed symmetric rates. ECCMAC is evaluated in this paper through theoretical analysis, extensive simulation, and simulation with measured data, and the results show that ECCMAC effectively improves wireless network performance.

Content aware optimization for video delivery over WCDMA

Abstract A content-aware networking framework for transmitting video on the uplink of a Wideband Code Division Multiple Access (WCDMA) cellular network is studied in this article. We consider a multi-user scenario and exploit the underlying structure of the video content to optimally schedule frames in order to minimize the total distortion of video quality across all users. In particular, we propose a novel Content-Aware Distortion Fair (CADF) scheme that determines, between multiple flows, the best set of frames to schedule using optimal transmit power, while meeting interference and delay constraints. The optimization problem is considered on the time scale of a single Group of Pictures, and is formulated as a restricted Multiple Knapsack Problem. A key contribution of this study is evaluating the CADF scheme on a Qualcomm 3G emulator, called “High data rate System Emulator 2” (HSE 2), and conducting rate control experiments with different types of emulated channel conditions. Our experimental results show that the CADF scheme significantly reduces video distortion, compared to the existing Foschini-Miljanic closed-loop distributed power control algorithm implemented on the WCDMA uplink. In the Appendix section, we also use the emulator to analyze the Traffic-to-Pilot resource allocation algorithm implemented on the reverse link of Evolution-Data Optimized (EV-DO) Revision-A by profiling over different traffic classes.

Development of a Hybrid Algorithm for Efficient Optimisation of Base Station Placement for Indoor Wireless Communication Systems

A new hybrid algorithm termed Reduction Estimation--Combinatorial Optimisation--Reduction Approximation is proposed to identify an optimal base station placement as a subset of a known set of potential sites to provide wireless communication services to a given set of stationary users. Both forward and reverse link signal-to-interference ratios are considered, and the performance of the proposed algorithm is reported for several representative case studies and compared with Brute Force Search and existing optimisation algorithms (including Genetic, Ngadiman and Greedy algorithms). For the cases considered, the proposed algorithm is found to be superior to the existing algorithms in that it can yield an optimal deployment (equivalent to Brute Force Search) in an acceptable time.

Bit Allocation and Statistical Precoding for Correlated MIMO Channels With Limited Feedback

In this paper, we jointly consider statistical precoding and feedback of bit allocation (BA) for multiple-input-multiple-ouput (MIMO) systems over correlated channels. The proposed system will be termed a BA system. We assume that the statistics of the channel is known to the transmitter and a reverse link of very low rate is available so that the receiver can send back the quantized BA. Based on the statistics of the channel, we derive the statistical precoder so that bounds of the error rate averaged over the random correlated channel are minimized. Due to statistical precoding, the distribution of the BA is highly nonuniform. Treating BA as a vector signal, we quantize it using vector quantization (VQ), which is known to be particularly useful for quantizing signals with nonuniform distributions. As the distribution of BA is taken into consideration in the codebook design, a good tradeoff between performance and feedback rate can be achieved. Simulations show that the combination of statistical precoding and VQ-based quantization for BA leads to good performance with a small number of feedback bits.

IN-BUILDING RADIO PROPAGATION AT 900 MHZ IN MULTI STORIED BUILDING

The proliferation of PCS has necessitated the complete characterization of radio channels existing inside buildings. The indoor radio channel differs from the conventional mobile radio channel in two aspects. First of all the distances taken in account are a lot small, and then the inconsistency of the environment is much larger for a smaller range of distance between transmitter and receiver. Indoor use of wireless systems poses one of the major design challenges, as indoor radio (RF) propagation is essentially a complex phenomenon. In this paper we will try to emphasis on this odd subject and will try to compute and place boundaries for use of wireless systems within buildings at 900 MHz. There are many good system design tools which have been developed solely for ground mobile cellular systems. However, no proper design tools have been developed for both ground mobile communication and in-building communications operated within one cellular system. As cellular systems are operated today, in-building communication is provided by transmitting radio signals from cell sites so that they penetrate the building walls to reach portable handsets inside buildings. In-building communication is harder to perform on the reverse link (portable-to-base link) than the forward link. Du to this it is difficult to mathematically put the model for all telecommunication systems in a single equation so many models coexist for different types of radio links for different situations. In this paper statically modelled is been explored. . The model rely on computing the median path loss for a link under a certain probability that the considered conditions will occur The modelling is done using simple measurements made especially for an intended communication system or spectrum allocation. This paper present radio signal propagation measurement and modelling at 900MHz, within a Hotel building in the city of Udaipur (India).

Performance effects of two-way FAST TCP

In this paper we study the performance of delay-based congestion control in the presence of queueing in the reverse path. Specifically, we consider FAST TCP in a single-bottleneck network by considering two scenarios, each corresponding to an equilibrium where a different direction of the bottleneck link is saturated. We argue that the local stability properties of FAST are unchanged by reverse traffic, and present expressions for the throughput of each flow and link. Finally, we consider the effect of bidirectional traffic on the dynamics of the number of flows in the network. We find conditions on the traffic loads under which the bottleneck shifts between the forward and reverse links, and conditions under which a given direction is always the bottleneck.

BER Performance Analysis of CDMA Reverse Link under AWGN Channel

bit error rate (BER) performance of the Code Division Multiple Access (CDMA) cellular system based on IS-95 standard in the presence of an additive white Gaussian noise (AWGN) and interference has been investigated in this paper. The performance is evaluated under two types of decision feedback receivers for the CDMA reverse link. These two feedback receivers are: (a) Hard decision Viterbi decoder in which coded bit is estimated based on Hamming Distance method and (b) Soft decision Viterbi decoder in which Euclidean Distance method is used for coded bit estimation. The comparison of these two techniques of decision feedback receivers of CDMA is done under AWGN channel. The performance of CDMA system is shown in graphs between BER versus Energy per bit to Noise Ratio i.e. Eb/No ratio. KeywordsBER, Chip Rate, Chip period, Eb/No, PN codes.

Does Frequent Low Resolution Feedback Outperform Infrequent High Resolution Feedback for Multiple Antenna Beamforming Systems?

Multiple antenna systems that adapt to the channel conditions are known to provide numerous rate and reliability benefits. In frequency division duplexing, the transmitter typically learns about the channel conditions using a small amount of feedback (called limited feedback) sent on the reverse link. While feedback is well studied, there has been only limited work addressing how feedback techniques should be modified depending on the amount of mobility. This paper concerns a signaling scheme for limited feedback multiple antenna wireless communications taking the temporal correlation into account during feedback design. We refer to this as using an adaptive feedback period (AFP) scheme. In the AFP scheme, the transmitter and receiver reuse the past channel state information (CSI) as side information. Feedback to be used for several channel uses is sent from the receiver to the transmitter using a predetermined feedback update period. The feedback update period is determined by characterizing the temporal correlation statistic, so that the proposed AFP scheme outperforms the traditional limited feedback approach, which we refer to as the minimal feedback period (MFP) scheme. To measure the performance, the average effective SNR is considered. Bounds on the feedback update period, correlation coefficient, and feedback rate needed for the AFP scheme to outperform the MFP scheme are derived. Moreover, criteria to initiate the control of the feedback update period are obtained. Results on the average effective SNR are used to develop bounds on the feedback update period using the capacity loss. It is also shown that in the large system limit the feedback update periods required for both the average effective SNR and capacity loss converge to the same bound. These results verify that infrequent high resolution feedback is sometimes preferable to frequent low resolution feedback.

Performance of a Distributed Full Inversion Power Control and Base Station Assignment Scheme in a Cellular CDMA Network with Hot-spots

In this article, a pilot power based power control (PPBPC) algorithm integrated with base station assignment is proposed, analysed and verified. It is decentralized, uses transmit power control and adapts cell sizes for load distribution. Unlike previously proposed algorithms in the literature, the proposed algorithm does not require prior knowledge of the channel gains between the users and the base stations. Each base station transmits its forward link pilot power inversely proportional to the total reverse link received power. The mobile station senses the strongest pilot power and determines its home base station. The proposed algorithm yields dynamic propagation of base station assignment--which leads to reassignment of home base stations system-wide reducing the total mobile transmit power. We also investigate the system performance various load conditions and show the advantage of load balancing in the cellular system. The simulation study shows that in a load balanced system, the maximum received power at the base stations is minimized which leads to interference balancing of the system.

Decoupled Power Allocation Through Pricing on a CDMA Reverse Link Shared by Energy-Constrained and Energy-Sufficient Data Terminals

We perform market-oriented management of the reverse link of a CDMA cell populated by data terminals, each with its own data rate, channel gain, willingness to pay (wtp), and link-layer configuration, and with energy supplies that are limited for some, and inexhaustible for others. For both types of energy budgets, appropriate performance indices are specified. Notably, our solution is "decoupled" in that a terminal can choose optimally, irrespective from choices made by the others, because it pays in proportion to its fraction of the total power at the receiver, which directly determines its signal-to-interference ratio (SIR), and hence its performance. By contrast, in other similarly-sounding schemes terminals' optimal choices are interdependent, which leads to "games of strategy", and their practical and theoretical complications. We study two situations: pricing for maximal (i) network revenue, and (ii) social benefit. The socially-optimal price is common to all terminals of a given energy class, and an energy-constrained terminal pays in proportion to the square of its power fraction. By contrast, the revenue-maximising network sets for each terminal an individual price that drives the terminal to the "revenue per Watt" maximiser. The network price is higher, and drives each terminal to consume less. Distinguishing features of our model are: (i) the simultaneous consideration of both limited and unlimited energy supplies, (ii) the performance metrics utilised (one for each type of energy supply), (iii) the generality of our physical model, which can lead to an optimal link-layer configuration, and (iv) our pricing of the received power fraction which yields a "decoupled" solution.

Efficient Partial Relaying Protocol for Wireless Multi-Hop Transmission

We propose a multi-hop transmission protocol suitable for the reverse link of cellular systems. The proposed protocol, referred to as cooperative multiplexing with partial relaying (CM-PR), is base...

Reverse Link Performance of DS-CDMA Cellular Systems through Closed-Loop Power Control, Base Station Assignment, and Antenna Arrays in 2D Urban Environment

The interference reduction capability of antenna arrays, base station assignment, and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. In this paper, we propose smart step closed-loop power control (SSPC) algorithm and base station assignment method based on minimizing the transmitter power (BSA-MTP) technique for direct sequence-code division multiple access (DS-CDMA) receiver in a 2D urban environment. This receiver consists of conjugate gradient adaptive beamforming and matched filter in two stages using antenna arrays. In addition, we study an analytical approach for the evaluation of the impact of power control error (PCE) on the DS-CDMA cellular systems. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly improve the network bit error rate in comparison with conventional methods. Our proposed methods can also significantly save total transmit power and extend battery life in mobile units. In addition, we show that the convergence speed of the SSPC algorithm is faster than that of conventional algorithms. Finally, we discuss two parameters of PCE and channel propagation conditions (path-loss parameter and variance of shadowing) and their effects on the capacity of the system via some computer simulations.

Robust End-to-End Available Bandwidth Estimation forInteractive Satellite networks

This paper presents an efficient and accurate available bandwidth estimation algorithm for satellite links which generally have long propagation delay. Either the method using the rate of returning ACKs or the method using timestamp option is adopted for the bandwidth estimation algorithms to enhance TCP performance in the literature. The method using the rate of returning ACKs, which is the most popular for the available bandwidth estimation for a TCP connection, is known to have the influences from the reverse link (TCP receiver to TCP sender) traffic variation, especially in the asymmetric satellite links. The bandwidth estimation method using packet sending time information from the TCP timestamp option also has the drawback that the influence of the bottleneck link presented in the forward path is not properly considered. To overcome these limits, our algorithm performs in two steps. A forward path delay is calculated at the sender with the receiver sending time for an ACK packet in the first step. And in the second step, the forward path delay is updated more delicately through removing unrelated part from the forward path delay, and is applied for available bandwidth estimation. The simulation results show that our algorithm can avoid the influence of the traffic variation in the return path (e.g., ACK compression, DAMA delay), and estimate the available bandwidth over the forward path more accurately. Satellite networks are becoming the important candidate in information and communication infrastructures because they provide several advantages to the wireless Internet communications. They generally provide wider coverage, higher bandwidth, and relatively faster establishment than other terrestrial wireless networks. Nevertheless, satellite links pose some challenges to the congestion control operation of the TCP (Transmission Control Protocol) (10). Main challenges of the satellite networks to the TCP performance are the long RTT (round-trip time) which is generally around 600msec in the bi-directional networks over the geostationary satellite, and the presence of the high packet loss rate by wireless random error which causes congestion control of the TCP spuriously. To solve the problems while keeping end-to-end semantics of TCP, an accurate bandwidth estimation algorithm is

Erlang Capacity Analysis of 3G/Ad Hoc Integrated Network

This letter presents an analytical study of the reverse link Erlang capacity of 3G/Ad Hoc Integrated networks. In the considered integrated network, 3G networks and Ad Hoc networks operate over the same frequency band and hence cause interference to each other. The reverse link Erlang capacity is analyzed and discussed in two cases: Ad Hoc networks use and do not use power control.

Reverse Link Performance of DS-CDMA Cellular Systems through Closed-Loop Power Control and Beamforming in 2D Urban Environment

The interference reduction capability of antenna arrays and the power control algorithms have been considered separately as means to decrease the interference in wireless communication networks. In this paper, we propose smart step closed-loop power control (SSPC) algorithm in direct sequence-code division multiple access (DS-CDMA) receivers in a 2D urban environment. This RAKE receiver consists of conjugate gradient adaptive beamforming (CGBF) and matched filter (MF) in two stages and finally, the output signals from the MFs are combined and then are fed into the decision circuit for the desired user. Also, we present switched-beam (SB) technique for enhancing signal to interference plus noise ratio (SINR) in network. Also, we study an analytical approach for the evaluation of the impact of power control error (PCE) on DS-CDMA systems in a 2D urban environment. The simulation results indicate that the convergence speed of the SSPC algorithm is faster than other algorithms. Also, we observe that significant saving in total transmit power (TTP) are possible with our proposed algorithm. Finally, we discuss two parameters of the PCE and path-loss exponent and their effects on capacity of the system via some computer.

Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.

Estimation of the carrier-to-interference ratio in the reverse link of the IMT-2000 cellular communications system

An algorithm for estimating the input carrier-to-interference ratio of the base station receiver of a mobile communications system has been developed. The estimation procedure is performed under the condition that multipath signals are received, multiple-access interference represents white Gaussian noise, and perfect clock synchronization is implemented. The algorithm is synthesized via the maximum-likelihood method. The results of simulation modeling are presented.

UHF RFID Systems; Their Susceptibility to Backscattered Signals Induced by Electronic Ballast Driven Fluorescent Lamps

It was demonstrated that high speed switching of electronic ballast driven fluorescent lamp (EBFL) reflects and modulates the incident UHF RFID forward link reader- tag signal in a manner similar to that of modulated reverse link backscattered tag-reader signal. Qualitative analysis of EBFL's backscattered radiation properties indicated it has a half dipole pattern similar to that of the UHF RFID tag. Its backscatter signal spectrum falls within the spectral band of the tag signal with power levels exceeding that of a tag-reader signal power when located at distances over 5 meters from the reader antenna. Performance analyses results of an operating UHF RFID system, in close proximity to a set of active EBFLs, indicated without any doubt that the EBFL's modulated backscattered signal is a source of strong interference. It can compromise the reverse link and significantly affect the reception of modulated backscattered UHF RFID tag signals. The effects of this interference must be taken into consideration when developing an RFID system operating in an environment abundant with EBFLs.

Computational modeling with forward and reverse engineering links signaling network and genomic regulatory responses: NF-κB signaling-induced gene expression responses in inflammation

BackgroundSignal transduction is the major mechanism through which cells transmit external stimuli to evoke intracellular biochemical responses. Diverse cellular stimuli create a wide variety of transcription factor activities through signal transduction pathways, resulting in different gene expression patterns. Understanding the relationship between external stimuli and the corresponding cellular responses, as well as the subsequent effects on downstream genes, is a major challenge in systems biology. Thus, a systematic approach is needed to integrate experimental data and theoretical hypotheses to identify the physiological consequences of environmental stimuli.ResultsWe proposed a systematic approach that combines forward and reverse engineering to link the signal transduction cascade with the gene responses. To demonstrate the feasibility of our strategy, we focused on linking the NF-κB signaling pathway with the inflammatory gene regulatory responses because NF-κB has long been recognized to play a crucial role in inflammation. We first utilized forward engineering (Hybrid Functional Petri Nets) to construct the NF-κB signaling pathway and reverse engineering (Network Components Analysis) to build a gene regulatory network (GRN). Then, we demonstrated that the corresponding IKK profiles can be identified in the GRN and are consistent with the experimental validation of the IKK kinase assay. We found that the time-lapse gene expression of several cytokines and chemokines (TNF-α, IL-1, IL-6, CXCL1, CXCL2 and CCL3) is concordant with the NF-κB activity profile, and these genes have stronger influence strength within the GRN. Such regulatory effects have highlighted the crucial roles of NF-κB signaling in the acute inflammatory response and enhance our understanding of the systemic inflammatory response syndrome.ConclusionWe successfully identified and distinguished the corresponding signaling profiles among three microarray datasets with different stimuli strengths. In our model, the crucial genes of the NF-κB regulatory network were also identified to reflect the biological consequences of inflammation. With the experimental validation, our strategy is thus an effective solution to decipher cross-talk effects when attempting to integrate new kinetic parameters from other signal transduction pathways. The strategy also provides new insight for systems biology modeling to link any signal transduction pathways with the responses of downstream genes of interest.

Channel estimation method using power control schemes in wireless systems

Green communication is a new paradigm of designing the communication system which considers not only the processing performance but also the energy efficiency. Power control management is one of the approaches in green communication to reduce the power consumption in distributed communication system. In this paper, we propose improved power control schemes for mobile satellite systems with ancillary terrestrial components (ATCs). In order to increase system capacity and reduce the transmitting power of the user's equipment, we propose an efficient channel estimation method consisting of a modified open-loop power control (OLPC) and closed-loop power control (CLPC). The OLPC works well if the forward and reverse links are perfectly correlated. The CLPC is sensitive to round-trip delay and, therefore, it is not effective in a mobile satellite system. In order to solve the above problem, we added monitoring equipment to both the OLPC and CLPC to use information about transmitting power that has not yet been received by the receiver over the satellite/ATC channel. Moreover, we adapted an efficient pilot diversity of both OLPC and CLPC in order to get a better signal to interference plus noise ratio estimation of the received signal.