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Publikacije (259)

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Iulia Prodan, Tatsunori Obara, F. Adachi, H. Gačanin

Broadband analog network coding (ANC) has been recently introduced to increase the network capacity by exploiting the broadcasting nature of the wireless channel. However, channel state information (CSI) knowledge is required for self-information removal and signal detection. Recently, a pilot-assisted channel estimation (PACE) scheme has been presented for broadband ANC, where feedback of the channel estimates from the relay to the users is required. In this work, we introduce a PACE scheme without feedback from the relay for broadband ANC using orthogonal frequency-division multiplexing (OFDM). In the first time slot the users transmit their respective pilots to the relay and in the second time slot the relay simply amplifies and forwards the received pilot signals to both users. Each user can then estimate all the CSI it needs for self-information removal and coherent signal detection, without requiring any feedback from the relay. The bit error rate (BER) performance of broadband ANC using the proposed PACE is evaluated by computer simulation. It was shown that the proposed PACE scheme causes only a slight BER performance degradation compared to the conventional PACE scheme while eliminating the feedback channel requirement.

H. Gačanin, Mika Salmela, F. Adachi

Network coding at the physical layer (PNC) can be used to improve the network capacity in a wireless channel. Broadband analog network coding (ANC) was introduced as a simpler implementation of PNC. The coherent detection and self-information removal in ANC require accurate channel state information (CSI). In this paper, we theoretically investigate an impact of the channel time-selectivity on the bit error rate (BER) performance of broadband ANC with practical channel estimation (CE) scheme using orthogonal frequency division multiplexing (OFDM). The achievable BER performance gains due to the first and second order polynomial time-domain channel interpolation are evaluated using derived close-form BER expressions.

Amir Ligata, H. Gačanin, F. Adachi, M. Smolnikar, M. Mohorčič

Orthogonal frequency division multiplexing (OFDM) is an effective technique for high-speed digital transmission over time-dispersive channels. However, for coherent detection, a reliable channel estimation (CE) is required. OFDM is characterized by its high peak-to-average power ratio (PAPR), which makes it very sensitive to nonlinear distortions that may affect the channel estimation accuracy leading to a bit error rate (BER) performance degradation. In this paper, we present closed-form BER expression for OFDM with a pilot-assisted CE in a nonlinear and frequency-selective fading channel. We discuss how, and to what extent, the nonlinear degradation affects the BER performance with the CE based on a time/frequency division-multiplexed (TDM/FDM) pilot. The analysis is based on a Gaussian approximation of the nonlinear noise due to both HPA amplitude limitation and quantization. We also evaluate the estimator's mean square error (MSE) with both TDM and FDM pilots. Our results show that pilot-assisted CE using FDM pilot is more sensitive to nonlinear distortions than the CE using a TDM pilot, since its pilot subcarriers are affected by nonlinear noise due to both the HPA and the quantization.

Iulia Prodan, 小原 辰徳, H. Gačanin, F. Adachi

Broadband analog network coding (ANC) has been recently introduced to further increase the network capacity by exploiting the broadcasting nature of the wireless channel. However, channel state information (CSI) knowledge is required for self-information removal and signal detection. Recently, a pilot-assisted channel estimation (PACE) scheme has been presented for broadband ANC; however, feedback of the channel estimates from the relay to the users is required. In this paper, we present a PACE scheme for broadband ANC, based on orthogonal frequency-division multiplexing (OFDM) radio access, without feedback from the relay. In the first time slot, the users transmit their respective pilots to the relay and then, in the second time slot, the relay amplifies and forwards the received pilot signals to both users. Each user can then estimate all the CSI it needs for self-information removal and signal detection, without requiring any feedback from the relay. The bit error rate (BER) performance of broadband ANC using the proposed PACE is evaluated by computer simulation. It was shown that the proposed PACE scheme can achieve almost the same BER performance as the conventional PACE scheme, while eliminating the feedback channel requirement.

H. Gačanin, Tomas Sjödin, F. Adachi

Recently, broadband analog network coding (ANC) was introduced for high-speed transmission over the wireless (frequency-selective fading) channel. However, ANC requires the knowledge of channel state information (CSI) for self-information removal and coherent signal detection. In ANC, the users' pilot signals interfere during the first slot, which renders the relay unable to estimate CSIs of different users, and, consequently, four time-slot pilot-assisted channel estimation (CE) is required to avoid interference. Naturally, this will reduce the capacity of ANC scheme. In this paper, we theoretically analyze the bit error rate (BER) performance of bi-directional broadband ANC communication based on orthogonal frequency division multiplexing (OFDM) radio access. We also theoretically analyze the performance of the channel estimator's mean square error (MSE). The analysis is based on the assumption of perfect timing and frequency synchronization. The achievable BER performance and the estimator's MSE for broadband ANC is evaluated by numerical and computer simulation. We discuss how, and by how much, the imperfect knowledge of CSI affects the BER performance of broadband ANC. It is shown that the CE scheme achieves a slightly higher BER in comparison with ideal CE case for a low and moderate mobile terminal speed in a frequency-selective fading channel.

H. Gačanin, Tomas Sjödin, F. Adachi

Recently, broadband analog network coding (ANC) was introduced for high-speed transmission over the wireless (frequencyselective fading) channel. However, ANC requires the knowledge of channel state information (CSI) for self-information removal and coherent signal detection. In ANC, the users’ pilot signals interfere during the first slot, which renders the relay unable to estimate CSIs of different users, and, consequently, four time-slot pilot-assisted channel estimation (CE) is required to avoid interference. Naturally, this will reduce the capacity of ANC scheme. In this paper, we theoretically analyze the bit error rate (BER) performance of bi-directional broadband ANC communication based on orthogonal frequency division multiplexing (OFDM) radio access. We also theoretically analyze the performance of the channel estimator’s mean square error (MSE). The analysis is based on the assumption of perfect timing and frequency synchronization. The achievable BER performance and the estimator’s MSE for broadband ANC is evaluated by numerical and computer simulation. We discuss how, and by how much, the imperfect knowledge of CSI affects the BER performance of broadband ANC. It is shown that the CE scheme achieves a slightly higher BER in comparison with ideal CE case for a low and moderate mobile terminal speed in a frequency-selective fading channel.

H. Y. Shwe, H. Gačanin, F. Adachi

Power efficiency is a key issue in wireless sensor networks due to limited power supply. Buffer management is also crucially important in the scenario where the incoming traffic is higher than the output link capacity of the network since a buffer overflow causes power waste and information loss if a packet is dropped. There are many available buffer management schemes for traditional wireless networks. However, due to limited memory and power supply of sensor nodes, the existing schemes cannot be directly applied in wireless sensor networks (WSNs). In this work, we propose a multilayer WSN with power efficient buffer management policy which simultaneously reduces the loss of relevant packets. Unlike the conventional WSNs which consider the whole network as single layer, we divide sensor network topology logically into three different layers, each layer associated with different information collected from sensing environment. We show that our proposed multi-layer WSN can reduce the relevant packet loss and power waste for retransmission of lost packets.

A. A. Florea, H. Gačanin, F. Adachi

Cooperative networking schemes provide spatial diversity gain (named cooperative diversity gain) using the antennas of spatially distributed users. Consistent research has been focusing on cooperative networks using orthogonal frequency division multiplexing (OFDM) and single carrier with frequency domain-equalization (SC-FDE). Coherent detection and frequency-domain equalization (FDE) require accurate channel estimation. In this paper, we present a performance comparison of cooperative OFDM relay network and cooperative SC-FDE relay network with pilot-assisted channel estimation. We consider a joint diversity combining and FDE in order to obtain a larger frequency diversity gain. When channel coding is used, cooperative OFDM relay network performs similarly to cooperative SC-FDE relay network in a frequency-selective fading channel.

H. Gačanin, Mika Salmela, F. Adachi

Broadcast nature of the wireless channel enables wireless communications to make use of network coding at the physical layer (PNC) to improve the network capacity. Recently, narrowband and later broadband wireless analog network coding (ANC) were introduced as a simpler implementation of PNC. The coherent detection and self-information removal in ANC require accurate channel state information (CSI). In this paper, we present the bit error rate (BER) performance analysis with imperfect CSI for broadband ANC using orthogonal frequency division multiplexing (OFDM). The effect of time-selectivity is also studied to investigate its effect on the BER performance. It is shown that the fading tracking is an important problem for self-information removal.

Tomas Sjödin, H. Gačanin, F. Adachi

Recently, broadband analog network coding (ANC) was introduced to utilize high-data rate transmission over the wireless - frequency selective fading - channel. However, ANC requires the knowledge of channel state information (CSI) for self-information removal and coherent signal detection. In this paper, we propose a two-slot pilot-assisted CE for bi-directional broadband ANC. In the first slot, two users transmit their respective pilots to the relay, where the users' pilot signals are designed to avoid the interference and consequently, allow the relay to estimate the CSIs from both users. During the second slot the relay broadcast its pilot signal to both users that estimate the corresponding CSIs. It was shown by computer simulation that, even with imperfect CSI, the BER performance of broadband ANC gives a satisfactory performance for a low and moderate mobile terminal speed in a frequency-selective fading channel.

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