Channel Quality Information Feedback Research Articles

Cross-Layer Performance Analysis of Downlink Multi-Flow Carrier Aggregation in Heterogeneous Networks

Multi-flow carrier aggregation (CA) is an emerging technique that is implemented to improve the capacity of cellular networks. In this paper, we study the cross-layer performance of user equipments (UEs) in heterogeneous networks under multi-flow CA. We develop a queuing analytical model for measuring packet-level performance parameters, e.g., packet loss probability and queuing delay. Our developed model accounts for the time-varying channels, the channel scheduling algorithm, partial channel quality information feedback, and the number of component carriers deployed at each tier. Our model also takes into consideration stochastic packet arrivals, the packet scheduling algorithm, and out-of-sequence packet delivery. The developed model can be used to tune the various system and operating parameters in order to offload traffic from the macrocells to the small cells while maintaining the quality of service requirements of UEs. The accuracy of the analytical model developed in this paper is validated through computer simulations.

Cross-Layer Performance of Downlink Dynamic Cell Selection With Random Packet Scheduling and Partial CQI Feedback in Wireless Networks With Cell Sleeping

In this paper, we consider a coordinated multipoint dynamic cell selection (DCS) transmission scheme for serving sleeping cell user equipments (UEs). According to this DCS scheme, packets of UEs in a sleeping cell are randomly forwarded to the potential active base stations (BSs) by the packet serving gateway and UEs in the sleeping cell dynamically select their serving BS from these active BSs. We model the system as a fork/join (F/J) queuing system and develop a cross-layer analytical model that considers the time varying nature of the channels, channel scheduling mechanism, partial channel quality information feedback, cell selection mechanism, bursty packet arrivals, and packet scheduling mechanism. The developed analytical model can be used to measure various packet-level performance parameters, such as packet loss probability (PLP) and queuing delay while accounting for out-of-sequence packet delivery. We validate the accuracy of the developed analytical model via simulations, and we compare the performance of the DCS scheme under consideration with the conventional fixed cell selection scheme and with the state-of-the-art DCS scheme. Presented numerical results show that the DCS scheme under consideration significantly improves the PLP performance. Queuing delay performance, on the other hand, depends on the system and operating parameters.

Limited Feedback Strategy For MU-MIMO Systems Under Spatially Correlated Channels

This paper studies limited feedback transmission strategy for downlink multiuser multiple-input multiple-output (MU-MIMO) systems under spatially correlated channels. To exploit the channel statistics for improving the performance of precoding at the base station (BS) with quantized channel direction information (CDI), we propose a two-level weighted DFT codebook (WDFT). It is composed of a long term DFT codebook representing the average CDIs and a short term codebook serving as an instantaneous weighting vector on them. The proposed codebook can adapt to various correlated channels without the need of channel correlation matrix at the BS. To mitigate the sum rate ceiling in high signal-to-noise ratio region caused by the quantized CDI with fixed size codebooks in less correlated channels, we propose a channel quality information (CQI) feedback strategy where each user helps the BS schedule users. By comparing its own CDI quantization error with a pre-determined threshold, each user feeds back one bit to indicate its preference of the transmission mode together with a corresponding CQI. With these information the BS first selects users separately from two user sets and finally selects users for downlink transmission. Simulation results show that the proposed limited feedback strategy including the WDFT codebook and the CQI feedback strategy outperforms existing schemes in various correlated channels.

Random neural network based cognitive engines for adaptive modulation and coding in LTE downlink systems

This paper presents two random neural network (RNN) based context-aware decision making frameworks to improve adaptive modulation and coding (AMC) in long-term evolution (LTE) downlink systems. In the first framework, AMC is modelled as a traditional classification problem with the aim to maximize the probability of correct classification. The second framework seeks to optimize the throughput as opposed to simply maximizing the probability of the correct classification. To model the second framework, we developed a hybrid cognitive engine (CE) architecture by integrating an RNN based learning algorithm with genetic algorithm (GA) based reasoning. RNN inherent properties help CE to comply with the essential CE design requirement (i.e. concurrent long-term-learning, low computational complexity, and fast decision making). The performance of RNN is compared with artificial neural networks (ANN) and state-of-the-art effective exponential SINR mapping (EESM) algorithm. A comprehensive analysis of the proposed RNN based AMC scheme is presented by jointly incorporating the effect of different schedulers, feedback delays, and multi-antenna diversity on the throughput of an orthogonal frequency-division multiple access (OFDMA) system. The critical analysis of the first framework revealed that RNN based CE can achieve comparable results with faster adaptation, even in severe environment changes without the need of retraining compared to ANN. The analysis of the second approach demonstrated RNNs faster adaptation as compared to ANN and showed upto 253% gain in user throughput. RNN based CE efficiently exploited the channel quality information feedback delay to improve system throughput and helped cell-edge and cell-centre users to experience much better services in terms of achieved throughput as compared to EESM.

Partial Channel Quality Information Feedback in Multiuser Relay Networks Over Nakagami- <inline-formula> <tex-math notation="LaTeX">$m$</tex-math></inline-formula> Fading

We propose a new partial feedback scheme in multiuser relay networks (MRNs) where a source communicates with $K$ destinations via a relay. We focus on a practical network model where orthogonal frequency division multiple access (OFDMA) is adopted in the downlink and only limited feedback overhead is supported in the uplink. For this model, we consider that the OFDMA spectrum consists of $M_{\mathrm{RB}}$ resource blocks (RBs). In the proposed scheme, the destinations feed back the channel quality information (CQI) for the best $M_{\mathrm{FB}}$ RBs, instead of all $M_{\mathrm{RB}}$ RBs, to the source through the relay, which fulfills the requirement of feedback overhead. Considering the highly versatile Nakagami- $m$ fading, we derive new closed-form expressions for the exact sum rate for ideal CQI feedback and quantized CQI feedback. We also derive the asymptotic sum rate expression for ideal CQI feedback. We have some new findings to understand the impact of network and channel parameters on the sum rate. First, a more scattering fading environment with a lower $m$ decreases the sum rate for a small $K$ , but increases the sum rate for a large $K$ . Second, the sum rate increases as ${M_{\mathrm{FB}}}$ approaches ${M_{\mathrm{RB}}}$ . Third, the sum rate gap between ideal CQI feedback and quantized CQI feedback increases when $M_{\mathrm{FB}}$ or $K$ increases. Fourth, we demonstrate that the proposed partial feedback scheme achieves almost the same sum rate as the full feedback scheme for a large number of destinations.

Opportunistic Spectrum Sharing With Limited Feedback in Poisson Cognitive Radio Networks

In this paper, we propose two limited feedback based underlay spectrum sharing schemes in Poisson cognitive radio networks without and with primary exclusive regions, respectively. Both primary and secondary transmitters are Poisson distributed nodes with limited feedback of channel quality information from their local receivers. The primary transmitters are active if their local primary channels are above a certain threshold. In the opportunistic spectrum sharing scheme without primary exclusive region, the secondary transmitters are elected to transmit if their local channels are above the required threshold. In the opportunistic spectrum sharing scheme with a primary exclusive region, the secondary transmitters transmit if their local channels are above the threshold and they are outside the exclusive regions of the active primary receivers. For both schemes, the optimal secondary node density is analytically derived by maximizing the secondary area spectral efficiency subject to the secondary outage constraint and the primary efficiency loss constraint. Numerical results show that, for a tight secondary outage constraint, it is more beneficial to use the scheme with no primary exclusive region. For relatively loose secondary outage constraint, the scheme with primary exclusive regions is recommended.

Exploiting Multiuser Diversity with 1-bit Feedback for Spectrum Sharing

In this paper, we propose a limited feedback based underlay spectrum sharing scheme where a downlink secondary network shares the spectrum with a pair of primary users. The primary receiver and N secondary receivers each sends 1-bit feedback of channel quality information to their corresponding transmitters. By overhearing the primary feedback and receiving the secondary feedback, one of the secondary receivers is scheduled at the secondary transmitter in each fading block. The optimal channel quantization thresholds and power allocation are jointly determined by maximizing the average throughput of the secondary user under the average secondary power constraint and the average primary rate loss constraint. The average throughput of the secondary user grows as log log N.

Impact of Feedback Channel Delay over Joint User Scheduling Scheme and Separated Random User Scheduling Scheme in LTE-A System with Carrier Aggregation

In Long Term Evolution-Advanced (LTE-A), the signal quality in a wireless channel is estimated based on the channel quality measurements. The measurement results are used to select suitable modulation and coding scheme for each transmission, feedback, and processing delay, which can cause a mismatch between channel quality information (CQI) and current channel state at the base station. However, prospect delays in the reception of such CQI may lead to a system performance degradation. This study analyzes the impact of CQI feedback delay on joint user scheduling (JUS) scheme and separated random user scheduling (SRUS) scheme in LTE-A system over carrier aggregation. The analysis will be compared with the system having delayed channel and perfect knowledge at different deployment scenario. We will study the throughput performance of both scheduling schemes with different deployment scenario, and then recommend the suitable deployment scenario to keep the desired QoS for a specific number of users. Results show that, in main beam directed at sector boundaries and diverse coverage, JUS scheme performs better than SRUS, which can justify the intensive use of user equipment power and extra control signaling overhead.

On the Asymptotic Throughput of OFDMA Systems with Best-M CQI Feedback

In order to enable channel-aware scheduling, orthogonal frequency-division multiple access (OFDMA) systems require each user to feed back channel quality information (CQI) relative to each frequency resource block (RB) toward the base station. 3GPP LTE systems relieve the overhead entailed by CQI feedback by employing the feedback scheme prescribing each user to report the index of the M best RB's along with one single CQI measure. In order to provide a flexible tool for system design, we derive an upper bound for the downlink throughput with best-M CQI feedback for both single and multi-antenna communication schemes. Asymptotic analysis shows that, for a large number of users, multiuser diversity provides an SNR gain that scales as 1/M.

On Hybrid ARQ and Quantized CSI Feedback Schemes in Quasi-Static Fading Channels

Recently, substantial attention has been paid to increase the achievable rates of wireless networks using different kinds of limited channel quality information feedback. Hybrid automatic repeat request (ARQ) and quantized channel state information (CSI) feedback are two well-known approaches applied by experts to provide the limited channel quality information at the transmitter. Considering quasi-static fading channels, this paper aims to provide some comparisons between the performance of these methods from different points of view. The paper first investigates the power- and outage-limited performance of hybrid ARQ and quantized CSI schemes under short- and long-term power constraints. Then, 1) the feedback signaling load, 2) robustness and 3) the complexity of these schemes are compared under short-term transmission power constraint. Both INcremental Redundancy (INR) and Repetition Time Diversity (RTD) approaches are considered for hybrid ARQ feedback. Finally, approximate low-complexity solutions are presented for power allocation in the INR ARQ-based scheme under long-term transmission power constraint. Analytical and numerical results demonstrate the equivalency or the superiority of these approaches in different circumstances.

Opportunistic Spectrum Sharing in Cognitive Radio Networks Based on Primary Limited Feedback

An opportunistic spectrum sharing scheme for a pair of secondary users co-existing with a pair of primary users is proposed in this letter. The primary user is considered to exploit the limited feedback of channel quality information (CQI) to allocate its transmission power and rate. By overhearing the limited feedback of the primary CQI, the secondary user accesses the channel with proper transmission power and rate while causing interference to the primary user. Under the primary rate loss constraint, the optimal transmit power and transmission rate for the secondary is obtained to maximize the secondary user throughput. Numerical results show that, with only 3 or 4 bits of feedback, the effective throughput of the secondary user is comparable to the case when both primary and secondary transmitters have the perfect CQI of the primary link.

Flexible block‐wise loading algorithm for effective resource allocation and reduction of uplink feedback information in OFDMA systems

AbstractAdaptive modulation and coding (AMC) is a well‐known technique that selects a suitable modulation level and coding rate according to the user's channel quality. The utilization of AMC in downlink (DL) requires the channel information of each user on DL to properly select the modulation and coding scheme (MCS) level. However, under a practical OFDMA system environment, it is unsuitable to feedback all the channel information over the whole frequency resources due to the limited uplink bandwidth. In this paper, to optimize the performance of the AMC system and to reduce the uplink feedback requirement, we propose a flexible block‐wise loading (FBL) algorithm combined with a novel channel quality information (CQI) feedback scheme requiring less number of CQI feedback bits, which is suitable for the general OFDMA system with AMC. The proposed FBL algorithm dynamically allocates groups of sub‐carriers to each user in DL based on the channel quality information encapsulated in a newly defined feedback signal format. As a result, the sector throughput and outage performance is improved due to the flexibility on the sub‐channel allocation and increased accuracy on the CQI feedback information by the proposed FBL algorithm. Copyright © 2008 John Wiley & Sons, Ltd.

Throughput analysis of multi-user OFDMA-systems using imperfect CQI feedback and diversity techniques

In this paper, the throughput of an adaptive multiuser SISO-OFDMA/FDD system with channel quality information (CQI) signalled digitized over a feedback channel to the transmitter is investigated, where the instantaneous signal-to-noise ratio (SNR) of the different subcarriers is used as CQI to exploit multi-user diversity using adaptive subcarrier allocation. The CQI available at the transmitter is assumed to be imperfect due to estimation errors and quantization at the receiver side, time delay and feedback errors. In this paper, a closed form expression of the average throughput of an adaptive multi-user OFDMA system using imperfect CQI and uncoded M-QAM modulation is derived. Furthermore, a closed form expression of the average throughput of an OFDMA system exploiting frequency diversity, which does not require CQI at the transmitter, is presented. Both throughput performances are compared in order to identify the optimal transmission strategy depending on the grade of CQI imperfectness.

Simple Dynamic Subcarrier Allocation With CQI Feedback Reduction for OFDMA Systems

The focus of this paper is a proposal for a computationally efficient dynamic subcarrier allocation (DSA) algorithm for orthogonal frequency-division multiple access (OFDMA) systems. The proposed DSA algorithm considerably reduces the computational complexity and the amount of channel quality information (CQI) compared to amplitude-craving greedy (ACG) algorithms, which use full CQI. At the same time, the performance of the proposed algorithm closely approaches that achieved by ACG algorithms. Moreover, the authors present a new bandwidth-assignment algorithm produced by modifying bandwidth assignment based on the signal-to-noise ratio (BABS). This modified BABS algorithm enables the proposed DSA algorithm to produce a strong outage performance gain over the conventional scheme.

Compression of Feedback for Adaptive Transmission and Scheduling

For wireless systems with adaptive modulation and/or scheduling, feedback of channel quality information is often necessary. It has been questioned whether the increased system performance is worth the additional feedback rate and the increased algorithm complexity. In this paper, we study how the feedback rate can be minimized, without losing the gains due to adaptive modulation and multiuser diversity. We present an in-depth study of the literature in the area, and evaluate the performance of several state-of-the-art channel quality feedback schemes. By illustrating the compromise between system throughput and feedback channel rate for various schemes, we are able to give valuable insight in choice of method for feedback rate reduction. A major conclusion is that for multicarrier systems, a lossy compression scheme is the best choice, while for single-carrier systems, schemes limiting feedback to only high-SNR users show good performance. Another conclusion is that there are still many issues to study before the schemes can be used in practice.

Methods for Compression of Feedback in Adaptive Multi-carrier 4G Schemes

In this paper, several algorithms for compressing the feedback of channel quality information are presented and analyzed. These algorithms are developed for a proposed adaptive modulation scheme for future multi-carrier 4G mobile systems. These strategies compress the feedback data and, used together with opportunistic scheduling, drastically reduce the feedback data rate. Thus the adaptive modulation schemes become more suitable and efficient to be implemented in future mobile systems, increasing data throughput and overall system performance.

Accepted from open call - Forward high-speed wireless packet data service in is-2000 - 1xev-dv

This article describes enhancements to the physical layer design of single-carrier (1×) cdma2000/sup /spl reg// wireless networks introduced by Revision C of the IS-2000 standard (commonly referred to as 1×EV-DV). These improvements are mainly for the support of high-speed wireless packet data service on the forward (base station to mobile station) link. A new shared channel, the forward packet data channel, F-PDCH, is introduced to significantly increase spectral efficiency. This is accomplished through smart, channel-dependent scheduling of base station, BS, resources by taking advantage of the delay-tolerant nature of data traffic. This shared channel utilizes fast link adaptation through adaptive modulation and coding supported by the feedback of channel quality information. A form of hybrid ARQ type II technique commonly referred to as asynchronous adaptive incremental redundancy compensates for frame error events due to imperfect link adaptation. The impact of the new channel on voice capacity of the system is designed to be minimal because the F-PDCH utilizes resources that are not consumed by real-time users.