Arash Behboodi

Experimental decomposition of the performance of fingerprinting-based localization algorithms

Despite their popularity, the current praxis of comparative experimental evaluation of fingerprinting-based localization algorithms is lacking rigor, with studies typically following an ad-hoc evaluation process and focusing on black-box comparison of complete algorithms. In this paper we present a systematic benchmarking methodology that is focused on gaining finegrained insight about the relative contributions of the individual phases of the fingerprinting-based localization algorithms to their overall performance. To this end, we decompose the localization algorithms in common phases (collection of raw measurements, creation of fingerprints, pattern matching and post-processing) and systematically asses the performance of different procedures that can be applied in each of these phases. We illustrate the application of the proposed methodology using a comprehensive experimental case-study of 3 WiFi fingerprinting algorithms with 4 raw RSSI collection procedures, 3 fingerprint creation and pattern matching procedures, 4 different post-processing procedures in 3 testbeds and 4 evaluation scenarios, resulting in 36 individual experiments. The results demonstrate that in the evaluated scenarios, a lower number of WiFi APs and rather simple fingerprint creation and pattern matching can achieve better performance in terms of location accuracy than more sophisticated alternatives. The results also show that postprocessing steps like k-Nearest Neighbours (kNN) procedure are indeed effective in reducing the localization error variability and extremes, thus increasing the stability of the location estimation.

Cooperative Strategies for Simultaneous and Broadcast Relay Channels

Consider the simultaneous relay channel (SRC) that consists of a set of relay channels where the source wishes to transmit common and private information to each of the destinations. This problem is recognized as being equivalent to that of sending common and private information to several destinations in presence of helper relays where each channel outcome becomes a branch of the broadcast relay channel (BRC). Cooperative schemes and capacity region for a set with two memoryless relay channels are investigated. The proposed coding schemes, based on decode-and-forward (DF) and compress-and-forward (CF), must be capable of transmitting information simultaneously to all destinations in such a set. Depending on the quality of source-to-relay and relay-to-destination channels, inner bounds on the capacity of the general BRC are derived. Three cases of particular interest are considered: 1) cooperation is based on DF strategy for both users, referred to as DF-DF region; 2) cooperation is based on CF strategy for both users, referred to as CF-CF region; and 3) cooperation is based on DF strategy for one destination and CF for the other, referred to as DF-CF region. These results can be seen as a generalization and hence unification of previous works. An outer bound on the capacity of the general BRC is also derived. Capacity results are obtained for the specific cases of semidegraded and degraded Gaussian SRCs. Rates are evaluated for Gaussian models where the source must guarantee a minimum amount of information to both users while additional information is sent to each of them.

On the asymptotic error probability of composite relay channels

Consider the composite relay channel consisting of a set of relay channels associated to a probability measure. The current channel is a draw from its probability and in some cases arbitrary small error probability cannot be guaranteed for all channels in the set. In this paper, instead of finding the maximum achievable rate subject to a small error probability (EP) for all the channels in the set, we look at the asymptotic behavior of EP for a given rate. The notion of achievable EP is introduced as a novel performance measure for wireless relay channels. We can intuitively define it as the smallest EP that can be asymptotically achieved for a given rate. The behavior of EP is directly related to the ∈-capacity of each channel in the set. It is shown that the behavior of EP is upper and lower bounded by the outage probability of a region which is referred to as the full error region. Then every code with a rate belonging to this region yields EP equal to one. Finally, new coding for oblivious cooperation simultaneously exploiting both Decode-and-Forward (DF) and Compress-and-Forward (CF) strategies is investigated. The Gaussian relay channel with slow fading is also discussed.

Selective coding strategy for unicast composite networks

Consider a composite unicast relay network where the channel statistic is randomly drawn from a set of conditional distributions indexed by θ ϵ Θ, which is assumed to be unknown at the source, fully known at the destination and only partly known at the relays. Commonly, the coding strategy at each relay is fixed regardless of its channel measurement. A novel coding for unicast composite networks with multiple relays is introduced. This enables the relays to select dynamically-based on its channel measurement - the best coding scheme between compress-and-forward (CF) and decode-and-forward (DF). As a part of the main result, a generalization of Noisy Network Coding is shown for the case of unicast general networks where the relays are divided between those using DF and CF coding. Furthermore, the relays using DF scheme can exploit the help of those based on CF scheme via offset coding. It is demonstrated via numerical results that this novel coding, referred to as Selective Coding Strategy (SCS), outperforms conventional coding schemes.

On the simultaneous relay channel with informed receivers

The simultaneous relay channel is investigated where the source is unaware of the channel statistic controlling the communication but knows that this statistic is one of two possible discrete memoryless relay channels. We aim to derive coding schemes capable of transmitting information, regardless of which of these relays is present. First, this problem is recognized as being equivalent to that of sending common and private information to two destinations in presence of two helper relays. In this scenario, each possible relay links becomes a branch of the so-called broadcast relay channel. An inner bound on the capacity region of this channel is derived. Applications of these results arise when the source node is uncertain of the noise levels or the network topology (e.g. due to user mobility the positions of the relay and the destination nodes are unknown). Specific rates are computed for an AWGN relay channel, where the relay node may be absent but the source node is unaware of this.

Interference Effect on Localization Solutions: Signal Feature Perspective

We study the effect of interference on localization algorithms through the study of the interference effect on signal features that are used for localization. Particularly, the effect of interference on packet-based Received Signal Strength Indicator (RSSI), reported by IEEE 802.11 and IEEE 802.15.4 technologies, and on Time of Flight (ToF), reported by IEEE 802.15.4 technology, is studied using both theoretical discussions and experimental verifications. As for the RSSI values, using an information theoretic formulation, we distinguish three operational regimes and we show that the RSSI values, in dBm, remain unchanged in the noise-limited regime, increase almost linearly with interference power in dBm in the interference- limited regime and cannot be obtained due to packet loss in the collision regime. The maximum observable RSSI variation is dependent on the transmission rate and Signal to Noise Ratio (SNR). We also show that ToF is, interestingly, decreased under interference which is caused in the symbol synchronization procedure at the receiver. After providing the experimental results, we discuss how the localization algorithms are affected by interference.

On the asymptotic spectrum of the error probability of composite networks

This paper investigates composite multiterminal networks which consist of a set of multiterminal channels indexed or parametrized by a vector of channel parameters θ. The channel in operation is drawn from the sample set with probability Pθ. Instead of finding the maximum achievable rate subject to a -asymptotically- small error probability (EP), we look at the behavior of the error probability for a fixed coding rate. The asymptotic spectrum of error probability (ASEP) is then introduced as a novel and more general performance measure for composite networks. Indeed, the ASEP is defined as the smallest probability that the EP exceeds a desirable error ε for a coding rate r. It is shown that the ASEP is directly related to the ε-capacity of the network and assuming memoryless channels the ASEP can be bounded by a new region referred to as the full error region. Moreover, every code with a rate belonging to this region yields asymptotic EP equal to one.

Capacity of a class of broadcast relay channels

Consider the broadcast relay channel (BRC) which consists of a source sending information over a two user broadcast channel in presence of two relay nodes that help the transmission to the destinations. Clearly, this network with five nodes involves all the problems encountered in relay and broadcast channels. New inner bounds on the capacity region of this class of channels are derived. These results can be seen as a generalization and hence unification of previous work in this topic. Our bounds are based on the idea of recombination of message bits and various effective coding strategies for relay and broadcast channels. Capacity result is obtained for the semi-degraded BRC-CR, where one relay channel is degraded while the other one is reversely degraded. An inner and upper bound is also presented for the degraded BRC with common relay (BRC-CR), where both the relay and broadcast channel are degraded which is the capacity for the Gaussian case. Application of these results arise in the context of opportunistic cooperation of cellular networks.

Jitter-Buffer Management for VoIP over Wireless LAN in a Limited Resource Device

VoIP over WLAN is a promising technology as a powerful replacement for current local wireless telephony systems. Packet timing Jitter is a constant issue in QoS of IEEE802.11 networks and exploiting an optimum jitter handling algorithm is an essential part of any VoIP over WLAN (VoWiFi) devices especially for the low cost devices with limited resources. In this paper two common algorithms using buffer as a method for Jitter handling are analyzed with relation to different traffic patterns. The effect of different buffer sizes on the quality of voice will be assessed for these patterns. Various traffic patterns were generated using OPNET and Quality of output voice was evaluated based on ITU PESQ method. It was shown that an optimum voice quality can be attained using a circular buffer with a size of around twice that of a voice packet.

Broadcasting over the relay channel with oblivious cooperative strategy

This paper investigates the problem of information transmission over the simultaneous relay channel with two users (or two possible channel outcomes) where for one of them the more suitable strategy is Decode-and-Forward (DF) while for the other one is Compress-and-Forward (CF). In this setting, it is assumed that the source wishes to send common and private informations to each of the users (or channel outcomes). This problem is relevant to: (i) the transmission of information over the broadcast relay channel (BRC) with different relaying strategies and (ii) the transmission of information over the conventional relay channel where the source is oblivious to the coding strategy of relay. A novel coding that integrates simultaneously DF and CF schemes is proposed and an inner bound on the capacity region is derived for the case of general memoryless BRCs. As special case, the Gaussian BRC is studied where it is shown that by means of the suggested broadcast coding the common rate can be improved compared to existing strategies. Applications of these results arise in broadcast scenarios with relays or in wireless scenarios where the source does not know whether the relay is collocated with the source or with the destination.