2,019 research outputs found
On the Performance of the Relay-ARQ Networks
This paper investigates the performance of relay networks in the presence of
hybrid automatic repeat request (ARQ) feedback and adaptive power allocation.
The throughput and the outage probability of different hybrid ARQ protocols are
studied for independent and spatially-correlated fading channels. The results
are obtained for the cases where there is a sum power constraint on the source
and the relay or when each of the source and the relay are power-limited
individually. With adaptive power allocation, the results demonstrate the
efficiency of relay-ARQ techniques in different conditions.Comment: Accepted for publication in IEEE Trans. Veh. Technol. 201
Relay Switching Aided Turbo Coded Hybrid-ARQ for Correlated Fading Channel
Hybrid-Automatic-Repeat-reQuest (HARQ) has become an indispensable technique in reliable communications systems. However, its performance is inevitably affected by the channelâs fading correlation. In this paper, we proposed a novel relay-switching aided HARQ scheme in order to mitigate the detrimental effects of correlated fading without unduly increasing the systemâs complexity and delay. Our results show that the proposed relay-switching regime operates efficiently in correlated channels, hence significantly reduces the error floor of turbo-coded HARQ. Additionally, a HARQ scheme using Segment Selective Repeat (SSR) is incorporated in the relay-switching scheme for achieving further improvements. Quantitatively, the proposed relay-switching aided turbo-coded HARQ scheme using SSR may achieve an approximately 2 dB gain, compared to the conventional amplify-and-forward aided turbo coded HARQ arrangement using Chase Combining. Index Terms - Relay switching, correlated fading channel, Hybrid-ARQ, turbo codes, chase combining, incremental redundancy, selective segment repeat
On the Interaction between TCP and the Wireless Channel in CDMA2000 Networks
In this work, we conducted extensive active measurements on a large nationwide CDMA2000 1xRTT network in order to characterize the impact of both the Radio Link Protocol and more importantly, the wireless scheduler, on TCP. Our measurements include standard TCP/UDP logs, as well as detailed RF layer statistics that allow observability into RF dynamics. With the help of a robust correlation measure, normalized mutual information, we were able to quantify the impact of these two RF factors on TCP performance metrics such as the round trip time, packet loss rate, instantaneous throughput etc. We show that the variable channel rate has the larger impact on TCP behavior when compared to the Radio Link Protocol. Furthermore, we expose and rank the factors that influence the assigned channel rate itself and in particular, demonstrate the sensitivity of the wireless scheduler to the data sending rate. Thus, TCP is adapting its rate to match the available network capacity, while the rate allocated by the wireless scheduler is influenced by the sender's behavior. Such a system is best described as a closed loop system with two feedback controllers, the TCP controller and the wireless scheduler, each one affecting the other's decisions. In this work, we take the first steps in characterizing such a system in a realistic environment
On the Required Number of Antennas in a Point-to-Point Large-but-Finite MIMO System: Outage-Limited Scenario
This paper investigates the performance of the point-to-point
multiple-input-multiple-output (MIMO) systems in the presence of a large but
finite numbers of antennas at the transmitters and/or receivers. Considering
the cases with and without hybrid automatic repeat request (HARQ) feedback, we
determine the minimum numbers of the transmit/receive antennas which are
required to satisfy different outage probability constraints. Our results are
obtained for different fading conditions and the effect of the power amplifiers
efficiency on the performance of the MIMO-HARQ systems is analyzed. Moreover,
we derive closed-form expressions for the asymptotic performance of the
MIMO-HARQ systems when the number of antennas increases. Our analytical and
numerical results show that different outage requirements can be satisfied with
relatively few transmit/receive antennas.Comment: Under review in IEEE Transactions on Communication
Green Communication via Power-optimized HARQ Protocols
Recently, efficient use of energy has become an essential research topic for
green communication. This paper studies the effect of optimal power controllers
on the performance of delay-sensitive communication setups utilizing hybrid
automatic repeat request (HARQ). The results are obtained for repetition time
diversity (RTD) and incremental redundancy (INR) HARQ protocols. In all cases,
the optimal power allocation, minimizing the outage-limited average
transmission power, is obtained under both continuous and bursting
communication models. Also, we investigate the system throughput in different
conditions. The results indicate that the power efficiency is increased
substantially, if adaptive power allocation is utilized. For instance, assume
Rayleigh-fading channel, a maximum of two (re)transmission rounds with rates
nats-per-channel-use and an outage probability constraint
. Then, compared to uniform power allocation, optimal power
allocation in RTD reduces the average power by 9 and 11 dB in the bursting and
continuous communication models, respectively. In INR, these values are
obtained to be 8 and 9 dB, respectively.Comment: Accepted for publication on IEEE Transactions on Vehicular Technolog
TCP over CDMA2000 Networks: A Cross-Layer Measurement Study
Modern cellular channels in 3G networks incorporate sophisticated power control and dynamic rate adaptation which can have significant impact on adaptive transport layer protocols, such as TCP. Though there exists studies that have evaluated the performance of TCP over such networks, they are based solely on observations at the transport layer and hence have no visibility into the impact of lower layer dynamics, which are a key characteristic of these networks. In this work, we present a detailed characterization of TCP behavior based on cross-layer measurement of transport layer, as well as RF and MAC layer parameters. In particular, through a series of active TCP/UDP experiments and measurement of the relevant variables at all three layers, we characterize both, the wireless scheduler and the radio link protocol in a commercial CDMA2000 network and assess their impact on TCP dynamics. Somewhat surprisingly, our findings indicate that the wireless scheduler is mostly insensitive to channel quality and sector load over short timescales and is mainly affected by the transport layer data rate. Furthermore, with the help of a robust correlation measure, Normalized Mutual Information, we were able to quantify the impact of the wireless scheduler and the radio link protocol on various TCP parameters such as the round trip time, throughput and packet loss rate
Joint Adaptive Modulation-Coding and Cooperative ARQ for Wireless Relay Networks
This paper presents a cross-layer approach to jointly design adaptive
modulation and coding (AMC) at the physical layer and cooperative truncated
automatic repeat request (ARQ) protocol at the data link layer. We first derive
an exact closed form expression for the spectral efficiency of the proposed
joint AMC-cooperative ARQ scheme. Aiming at maximizing this system performance
measure, we then optimize an AMC scheme which directly satisfies a prescribed
packet loss rate constraint at the data-link layer. The results indicate that
utilizing cooperative ARQ as a retransmission strategy, noticeably enhances the
spectral efficiency compared with the system that employs AMC alone at the
physical layer. Moreover, the proposed adaptive rate cooperative ARQ scheme
outperforms the fixed rate counterpart when the transmission modes at the
source and relay are chosen based on the channel statistics. This in turn
quantifies the possible gain achieved by joint design of AMC and ARQ in
wireless relay networks.Comment: 5 pages, 4 figures, To appear in the Proceedings of the 2008 IEEE
International Symposium on Wireless Communication Systems (ISWCS), Rykevick,
Island, Oct 200
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