Arie Koppelaar

Correcting systematic mismatches in computed log-likelihood ratios

A log-likelihood ratio (LLR) measures the reliability (and uncertainty) of a binary random variable being a zero versus being a one. LLRs are used as input in many implementations of decoding algorithms which also output LLRs. Mismatches in the outputs are, for example, generated by a decoder which is implemented by using approximations during its computations e.g. the symbol-by-symbol max-log a posteriori probability (APP) algorithm versus the correct forward-backward (log-APP) algorithm or Hagenauers approximation of the box function. We propose post-processing of output LLRs to correct part of the mismatches. This post-processing is a function of the statistics of the input LLRs. As examples, we study the effect of incorrectly scaled inputs to the box function leading to mismatched outputs, Hagenauers approximation to the box function, and the effect of compensating mismatches of LLRs on the performance of iterative decoders. Copyright

IP-recovery in the DVB-H link layer for TV on mobile

Recently, DVB-H Internet Protocol based TV on Mobile devices made its entrance in the mobile arena. Due to transmission over an error-prone channel, IP datagrams (packet at network layer) may be corrupted. To improve reception robustness, the DVB-H link layer is equipped with Forward Error Correction (FEC), allowing correction of erroneous IP datagrams, using two-bit signaling information. During reception, locator information is derived prior to FEC, indicating the storage position of correctly received IP datagrams. This is essential due to the variable-length sizes of the IP-based data. For the situation that FEC fails to correct all erroneously received data, the locator information enables retrieval of all correctly received IP datagrams and indicates the location of potentially corrected IP datagrams. Using the derived locator information, experimental research has shown that after FEC, a considerable number of correct IP datagrams can still be recovered from an incorrect MPE-FEC frame. This results in up to 50% data recovery for medium-sized datagrams. This successful recovery depends on the received IP datagram length and the transmission error probability and results in an improved audiovisual decoding quality.

High rate reconciliation

We discuss several concepts leading to a new reconciliation algorithm. It can be used in general settings, and uses soft decision techniques. High fates are already obtained for small block lengths.

Quantum key agreement

We consider quantum key agreement between two users Alice and Bob in which an eavesdropper Eve intercepts and resends photons. We show how Alice and Bob attain a probabilistic upper bound on Eves knowledge.

Simultaneous zero-tailing of parallel concatenated codes

In a parallel concatenated convolutional code, an information sequence is encoded by a convolutional encoder, and an interleaved version of the information sequence is encoded by another convolutional encoder. We discuss the situation in which we require both convolutional encoders to end in the all-zero state. To do so, we have to split an information word in two parts. One part contains the true information bits, and the second part contains the so-called tail bits, which are special bits with values computed such that both encoders end in the all-zero state. Depending on the interleaver, a different number of tail bits are needed. By using a constructive method, we give a characterization of all interleavers for a prescribed number of tail bits. We explain the method of encoding. In addition, simulations have been carried out to investigate the performance of codes resulting from simultaneous zero-tailing. This shows that simultaneous zero-tailing is similar in performance as compared to previously known zero-tailing methods (but with fewer trellis termination bits) and that it is better than zero-tailing just one of the encoders.

Hierarchical Subchannel Allocation for Mode-3 Vehicle-to-Vehicle Sidelink Communications

In this poster we present a graph-based hierarchical subchannel allocation scheme for V2V sidelink communications in Mode-3. Under this scheme, the eNodeB allocates subchannels for in-coverage vehicles. Then, vehicles will broadcast directly without the eNodeB intervening in the process. Therefore, in each communications cluster, it will become crucial to prevent allocation conflicts in time domain since vehicles will not be able to transmit and receive simultaneously. We present a solution where the time-domain requirement can be enforced through vertex aggregation. Additionally, allocation of subchannels is performed sequentially from the most to the least allocation-constrained cluster. We show through simulations that the proposed approach attains near-optimality.

Poster: Resource Allocation with Conflict Resolution for Vehicular Sidelink Broadcast Communications

In this paper we present a graph-based resource allocation scheme for sidelink broadcast V2V communications. Harnessing available information on geographical position of vehicles and spectrum resources utilization, eNodeBs are capable of allotting the same set of sidelink resources to different vehicles distributed among several communications clusters. Within a communications cluster, it is crucial to prevent time-domain allocation conflicts since vehicles cannot transmit and receive simultaneously, i.e., they must transmit in orthogonal time resources. In this research, we present a solution based on a bipartite graph, where vehicles and spectrum resources are represented by vertices whereas the edges represent the achievable rate in each resource based on the SINR that each vehicle perceives. The aforementioned time orthogonality constraint can be approached by aggregating conflicting vertices into macro-vertices which, in addition, reduces the search complexity. We show mathematically and through simulations that the proposed approach yields an optimal solution. In addition, we provide simulations showing that the proposed method outperforms other competing approaches, specially in scenarios with high vehicular density.