waashk/dblp huggingface dataset:
receive antenna gain of uniform linear arrays of isotrops. the receive antenna gain of an antenna array critically depends on the receiver noise covariance. receiver noise essentially originates from two sources: the receive low-noise amplifiers (lna), and background radiation that is received by the array. in case that the lnas are the sole origin of noise, it is state of the art to argue that the receiver noise is spatially uncorrelated, for noise originates in components of physically separate lnas. however, this argument ignores coupling between antennas due to their spatial proximity, and moreover the coupling introduced by the impedance matching network which is located between the antenna outputs and the lna inputs. because of these coupling effects, the receiver noise is usually spatially correlated even when independent lnas are the sole source of noise in the system. the noise covariance, depends on the following four factors: 1) antenna spacing of the array, 2) properties of the impedance matching network, 3) noise-resistance of the lnas, 4) intensity of received background noise with respect to noise generated by the lnas. taking these issues into account, we derive, in this paper, the receive antenna gain of a uniform linear antenna array of isotrops in closed form. it turns out that the receive antenna gain can become much larger than the number of antennas. for the case of low noise-resistance, and low relative intensity of received background noise, we show that the receive antenna gain can even grow exponentially with the number of antennas. these results are exciting, because they imply that the performance of communication systems which use multiple receive antennas can be much better than previously reported.
a compressed sensing based ultra-wideband communication system. sampling is the bottleneck for ultra-wideband (uwb) communication. our major contribution is to exploit the channel itself as part of compressed sensing, through waveform-based pre-coding at the transmitter. we also have demonstrated a uwb system baseband bandwidth (5 ghz) that would, if with the conventional sampling technology, take decades for the industry to reach. the concept has been demonstrated, through simulations, using real-world measurements. realistic channel estimation is also considered.
on the performance of amplify-and-forward cooperative diversity with the nth best-relay selection scheme. cooperative-diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. in this paper, we consider the amplify-and-forward cooperative-diversity system with the nth best-relay selection scheme. in the best-relay selection scheme, the best relay only forwards the source signal to the destination. however, the best relay might be unavailable; hence we might resort to the second, third or generally the nth best relay. we derive closed-form expressions for the symbol error probability, outage probability and channel capacity. in particular, we derive a closed-form expression for the probability density function of the signal-to-noise ratio of the relayed signal at the destination node. then, we find a closed-form expression for the moment generating function of the total snr at the destination. this mgf is used to derive the closed-form expressions of the performance metrics. results show that with the nth best relay the diversity order is equal to (m - n +2) where m is the number of relays. simulation results are also given to verify the analytical results.
multi-hop capacity of mimo-multiplexing relaying in wimax mesh networks. one of the main challenges for metro-scale wimax mesh network deployments is related to capacity scaling. in a full mesh mode, a wimax node acts as a mesh router as well as a client access node. to improve latency and speed performance, typical dual- and multi-radio mesh solutions use different radio channels to create separate links for access and mesh relaying services. the available spectrum is therefore split between mesh and client access services. network operators operating the wimax system over the licensed spectrum are not keen to provide separate radio channels for access and mesh relay services, as this reduces the total number of users serviced per spectrum allocation. mimo-multiplexing relaying approach however provides separate links for access and mesh relaying services on the same radio channel. in this paper, we discuss the multi-hop capacity of ofdm-based mimo-multiplexing relaying in wimax networks. for an n×n mimo-multiplexing relaying with amplification factor α at relay nodes, r-hops relaying degrade the capacity by at most -nlog2(α2r/(1+σrr=1 α2r nr)) +rnlog2(n) bits/sec/hz. therefore, greater capacity loss is experienced in networks employing high-order mimo-multiplexing relaying. we also show that the capacity loss is independent of the ofdm configurations employed; thus network operators could employ higher ofdm configurations to compensate data rate loss in access services when some of the mimo-multiplexing links are dedicated to mesh relay. this analysis provides useful guidelines for operators planning mimo-multiplexing option for mesh support in wimax network.
help: // hypertext in-emergency leveraging protocol. this paper proposes help://, a simple light-weight protocol that runs over http and is used to disseminate information from a server(s) to its clients during the time of a crisis. help runs on an architecture that is a hybrid mix between a pure client/server architecture and a peer-to-peer architecture. its resemblance to one versus the other is dynamically decided based on load. in particular, under light load, help operates in a client/server mode, where all clients are served directly from the server. under high load, however, help picks one client in every n clients to help the server in serving its content. the value of n is chosen dynamically to optimize the performance of help and to ensure that clients receive their requested content with a very high probability, even in the presence of uncooperative clients. we assess the performance of help through analysis, simulation experiments and real implementation in linux. we envision help to be installed as a plug-in in common browsers.
multiuser extensions for closed loop transmit diversity in hsdpa. closed loop transmit diversity has already been adopted by 3gpp for mimo hsdpa in the form of txaa and its dual stream counterpart, d-txaa. while both these transmission techniques provide performance gains for single user (su) scenarios, they both introduce multi-user interference in the downlink in multi-user(mu) scenarios. in this paper, we study the extension of these transmission techniques to the multi-user case which entail minimal changes to the existing standard. to this end, we consider the classical mmse chip equalizer receivers that feed back beamforming weights so as to maximize the receive sinr at each user equipment (ue). given that the base station (bs) has to use these weights to transmit data to the ues, we compare practical and realistic strategies that bs can employ in order to maximize downlink capacity. we derive the sinr expression for mmse chip equalizer receivers for the general case of mu-txaa which is used at the receivers to select optimum feedback weights. we investigate different multiuser schemes for hsdpa in the downlink (dl), compare their performance and suggest optimal strategies for single and dual stream transmission for both single and multi-antenna receivers and corroborate our arguments with simulation results. we show that for the case of single antenna receivers, scheduling users with same beamforming weights maximizes downlink capacity in txaa. for the d-txaa with multiple antennas at receivers (mimo) we show that sdma outperforms spatial multiplexing in terms of maximizing dl capacity.
a simple near-capacity bandwidth-efficient coded modulation scheme in rayleigh fading. this paper proposes a near-capacity yet simple bit-interleaved coded modulation with iterative decoding (bicm-id) scheme by employing a multi-dimensional (multi-d) mapping technique in a multi-d constellation carved from a rotated lattice. using extrinsic information transfer (exit) charts, it is shown that the proposed technique fits well with simple convolutional codes in terms of the area property, for which turbo pinch-off can happen at a low eb/no value. in particular, both exit chart analysis and simulation results indicate that by using just a simple convolutional code together with a 4-d mapping, a turbo pinch-off and a bit error rate (ber) close to 10-6 happen at a signal-to-noise ratio (snr) that is even lower than the bicm constraint capacity limit with a uniform input. the proposed bicm-id scheme can be considered as an attractive alternative to other bandwidth-efficient coded modulation techniques using powerful turbo-like codes such as turbo or low-density parity-check (ldpc) codes over a rayleigh fading channel.
multi-user joint subchannel and power resource-allocation for powerline relay networks. this paper investigates orthogonal frequency-division multiple-access (ofdma) resource-allocation schemes for two-hop relays in a home powerline communication (plc) network. unlike wireless channels, which can have noticeable path loss and shadow effects to bring a substantial relay gain, the powerline channel usually observes a quality of the relay channel on par with the direct link so that simple fixed relay configurations often lose performance instead of gaining any. besides, the quasi-cyclostationary powerline channel benefits little from diversity combining, a scheme often found in cooperative wireless relay protocols to obtain performance improvements on fast fading channels. to address these special and challenging features of the powerline channel, home-plc relay protocols that jointly allocate subchannels and power to the source and relay nodes are proposed. simulation results show that significant improvements of data rates can be achieved by jointly optimizing the subchannel and power allocation of home-plc relay networks.
achieving and maintaining cost-optimal operation of a hierarchical dht system. although hierarchical p2p systems have been found to outperform flat systems in many respects, current p2p research does not focus on strategies to build and maintain such systems. available solutions assume either no or little coordination between peers, that could lead the system toward satisfying a globally defined goal (e.g., minimizing traffic). in this paper we focus on hierarchical dhts and provide a full set of algorithms to build and maintain such systems, that mitigate this problem. in particular, given the goal state of minimizing the total traffic without overloading any peer, our algorithms dynamically adjust the system state as to keep the goal met at any time. the algorithms are fully decentralized and probabilistic, all decisions taken by the peers are based on their partial view on a set of system wide parameters. thus, they demonstrate the main principle of self-organization - the system behavior emerges from local interactions. our simulations, run in a range of realistic settings, confirm a good performance of the algorithms.
simulation of spit filtering: quantitative evaluation of parameter tuning. a future where internet telephony will constitute a target valuable to attack is not so unrealistic. e-mail spam botnets software can be updated to send voice spam (commonly referred to as spit, spam over internet telephony) constituting a huge threat to voip-based applications and business. this paper tries to learn from one of the biggest lessons learnt from the e-mail world, i.e. "do not wait until is too late", and proposes a quantitative study, based on a simulation campaign, of spit filtering based on the analysis of the call setup protocols. after discussing attack scenarios based on dichotomic choices by the attacker, it presents how the spit filtering system can be optimized in order to self-tune parameters achieving high spit detection ratio and low false rates at the same time.
joint transmission with significant csi in the downlink of distributed antenna systems. interference management is required for improving the performance of future mobile radio communication systems. in the downlink (dl) of cellular systems with base stations (bss) located in the cell centers and equipped with omnidirectional antennas, transmission strategies such as matched filtering (mf) can't achieve good system performance, and zero forcing (zf) with full channel state information (csi) of the whole system imposes a high computational cost and requires a substantial amount of feedback. in this paper, an intelligent signal processing technique with moderate complexity, i.e., zf joint transmission (jt) with significant csi, based on distributed antenna systems (dass) with bss located at three vertices of each cell and equipped with sector antennas is proposed. from numerical results, it is shown that our proposal is a good combination of bs antenna layout and signal processing technique for interference management. the proposed intelligent signal processing technique can significantly benefit from the proposed smart bs antenna layout.
linear precoding for multiuser mimo systems with multiple base stations. linear precoding for multiuser multiple input multiple output (mimo) cellular systems has generally focused on a single isolated cell. a crucial tool in algorithm development has been a downlink/uplink duality. here we investigate downlink multiuser communications across multiple cells. previous work identified the resulting asynchronous interference as a key issue. we prove the existence of a downlink/uplink duality requiring time reversal. this duality is used to develop an effective linear precoding algorithm for multiuser, multi-cell, mimo systems. simulation results illustrate the importance of accounting for, and to quantify the loss due to, asynchronous interference.
two-tx precoding codebooks for variable spatial correlation. we design precoding codebooks for the situation when the spatial correlation is not known at the transmitter, but its distribution is. the optimum codebooks combine features of grassmannian precoding, optimum in the limit of spatially i.i.d. channels, and equatorial precoding, where all antennas transmit the same power. parametrizable families of codebooks interpolating between these two are considered. the optimum choice of parameter depends on the distribution of spatial correlations. in the case of two transmit antennas, the interpolation is between sphere packings in 2d and sphere packings in 1d, and the codebooks can be understood as the vertices of deformed platonic solids.
a novel relay placement mechanism for capacity enhancement in ieee 802.16j wimax networks. the ieee 802.16j draft proposes a multi-hop relay network architecture that introduces the new network element of relay station aimed at increasing the network throughput or coverage. the deployment of the relay stations is one of the most important issues that determines the network throughput. given a base station, k relay stations, and a deployed region that can be fully covered by the bs, this paper proposes a relay deployment mechanism that determines the deployed locations of rss so that the bandwidth requirement of mss can be satisfied while the network throughput can be significantly improved. experimental study reveals that the proposed mechanism can efficiently determine the locations for relay deployment and improve the network throughput.
bidirectional packet aggregation and coding for voip transmission in wireless multi-hop networks. this paper proposes bidirectional packet aggregation and coding (bipac), a packet mixing technique which jointly applies packet aggregation and network coding in order to increase the number of supportable voip sessions in wireless multi-hop networks. bipac applies network coding for aggregated voip packets by exploiting bidirectional nature of voip sessions, and largely reduces the required protocol overhead for transmitting short voip packets. we design bipac and related protocols so that the operations of aggregation and coding are well-integrated while satisfying the required quality of service by voip transmission, such as delay and packet loss rate. our computer simulation results show that bipac can increase the number of supportable voip sessions maximum by around 70% as compared with the case when the packet aggregation alone is used, and 450% in comparison to the transmission without aggregation/coding. we also implement bipac in a wireless testbed, and run experiments in an actual indoor environment. our experimental results show that bipac is a practical and efficient forwarding method, which can be implemented into the current mesh hardware and network stack.
mapping techniques for uwb positioning. this paper deals with a wireless indoor positioning problem in which the location of a tag is estimated from range measurements taken by fixed beacons. the measurements may be affected by non-line-of-sight (nlos) errors that must be mitigated. we discuss a maximum likelihood (ml) positioning technique that assumes a realistic model for the range errors and a signature database providing information on the propagation conditions at every hypothesized tag spot. the database can be gathered from knowledge of the service area infrastructure and through pre-measurements. it is given in the form of a map indicating, at any node of a close-mesh grid, the nature (los/nlos) of the link between that node and each beacon. the performance of the positioning algorithm is assessed by simulation and is compared with other methods available in literature. the results show that the proposed technique provides significant improvements and is robust against mismatches between true and assumed values of the parameters in the range error model. comparisons with the cramer-rao bound are made.
robust multiplicative audio and speech watermarking using statistical modeling. in this paper, a semi-blind multiplicative watermarking approach for audio and speech signals has been presented. at the receiver end, the optimal maximum likelihood (ml) detector aided by the channel side information for gaussian and laplacian signals in noisy environment is designed and implemented. the performance of the proposed scheme is analytically calculated and verified by simulation. then, we adapt the proposed scheme to speech and audio signals. to improve robustness, the algorithm is applied to low frequency components of the host signal. besides, the power of the watermark is controlled elegantly to have inaudibility using perceptual evaluation of audio quality (peaq) and perceptual evaluation of speech quality (pesq) algorithms. experimental results over several audio and speech signals show the higher robustness of the proposed technique in comparison with a recent watermarking scheme.
using gmm and svm-based techniques for the classification of ssh-encrypted traffic. when employing cryptographic tunnels such as the ones provided by secure shell (ssh) to protect their privacy on the internet, users expect two forms of protection. first, they aim at preserving the privacy of their data. second, they expect that their behavior, e.g., the type of applications they use, also remains private. in this paper we report on two statistical traffic analysis techniques that can be used to break the second type of protection when applied to ssh tunnels, at least under some restricting hypothesis. experimental results show how current implementations of ssh can be susceptible to this type of analysis, and illustrate the effectiveness of our two classifiers both in terms of their capabilities in analyzing encrypted traffic and in terms of their relative computational complexity.
improved estimation of clock offset in sensor networks. clock synchronization is an important issue for the design of a network composed of small sensor nodes. based on the two-way timing message exchange mechanism and assuming an exponential network delay distribution, many analytical results have been presented in the literature by applying the techniques from statistical signal processing. this paper derives the minimum variance unbiased estimator for the clock offset for both symmetric and asymmetric exponential delay cases. for the asymmetric delays, it is shown to be a function of both the minimum and the mean link delays. this result is a very significant contribution since only the minimum link delay observations have been used to estimate the clock offset in the past. for the symmetric case, it is shown to coincide with the maximum likelihood estimator. in addition, the result is also applicable to clock synchronization problem in general computer networks.
starburst ssd: an efficient protocol for selective dissemination. we present starburst, a routing-based protocol designed to efficiently disseminate data items to small subsets within a sensor network. starburst constructs a routing hierarchy to enable fast, efficient and reliable dissemination to nodes in a sensor network that satisfy data-specific predicates. the protocol is based on the idea that when only a few nodes need an update, it is more efficient and much faster to route to those nodes directly. when every node needs an update, algorithms such as trickle are more efficient. starburst therefore dynamically determines what portion of nodes need an update and locally adapts its delivery policy accordingly. we also present dynamic beacon selection algorithms which enable scalability and fault tolerance in starburst. we have implemented and evaluated starburst on top of both the bvr and s4 routing protocols with promising results. our simulations show that starburst reduces both the transmission cost and latency of existing dissemination protocols by at least 50% for small subsets of nodes, and performs no worse than them for larger sets. finally, tests on the motelab testbed validate our simulation results.
on concurrent multipath transfer in sctp-based handover scenarios. handling mobility at the transport layer is a promising approach to achieve seamless handover in the context of heterogeneous wireless access networks. in particular, features such as multihoming and dynamic address reconfiguration provided by mobile sctp (msctp) protocol are among the key enablers for handover support at the transport layer. this paper investigates the applicability of concurrent multipath transfer (cmt) to distribute data among two end-to-end paths of an msctp association during the handover transition process. to that end, the principles of the msctp-cmt design are given, emphasizing the consequences of a sender-introduced reordering and its effect on congestion control. the proposed msctpcmt handover scheme is benchmarked with two other handover schemes, namely msctp and sctp failover-based. provided analysis indicates the possible application area of msctp-cmt, taking into account not only handover scenario parameters (dwelling time, available bandwidth ratio and round-trip time), but also an important design constraint: receiver buffer (rbuf) size. rbuf size proves to be a major limiting factor shrinking significantly, yet not excluding msctp-cmt's application scope.