Search

This paper considers the transmission of scheduling information in orthogonal frequency-division multiple-access (OFDMA)-based cellular communication systems such as the Third-Generation Partnership Project (3GPP) long-term evolution (LTE). These systems provide efficient usage of radio resources by allowing users to be dynamically scheduled in both frequency and time. This requires considerable amounts of scheduling information to be sent to the users. This paper compares two basic transmission strategies: transmitting a separate scheduling message to each user versus broadcasting a joint scheduling message to all users. Different scheduling granularities are considered, as are different scheduling algorithms. The schemes are evaluated in the context of the LTE downlink using multiuser system simulations, assuming a full-buffer situation. The results show that separate transmission of the scheduling information requires a slightly lower overhead than joint broadcasting when proportional fair scheduling is employed and the users are spread out over the cell area. The results also indicate that the scheduling granularity standardized for LTE provides a good tradeoff between scheduling granularity and overhead. [ABSTRACT FROM PUBLISHER]

When adopting transmit diversity in the Chinese digital television terrestrial broadcasting (DTTB) system, there exists two kinds of interference: training sequences (TSs) from different transmit antennas are overlapped; and the TSs are interfered with OFDM data due to multipath fading. In order to distinguish different TSs, this paper proposes a method to design orthogonal TS set, which also have good correlation characteristic. Subsequently, an iterative algorithm to eliminate the interference between TSs and data is proposed and theoretically analyzed. Finally, simulations are performed and the results show that the system with the proposed scheme can achieve great diversity gain under acceptable computational complexity. [ABSTRACT FROM PUBLISHER]

Transmit diversity can be applied to OFDM systems by adopting space time code. Since the received signal is the overlapped signals transmitted from different transmit antennas, channel estimation is a rather challenging task for space time coded OFDM (ST-OFDM) systems. Pilot structure can help the receiver to effectively separate the overlapped signals and perform accurate channel estimation. In this paper, we propose three different channel estimation algorithms based on specially designed comb type pilots inserted in frequency domain. One of our proposed algorithms is performed in frequency domain and the other two are performed in time domain. Such comb type pilot based algorithms can provide higher bandwidth efficiency than common significant-tap-catching algorithm using training block pilots. Numerical analyzes and computational simulation show that our proposed estimation schemes have the same good performance while the time domain methods have relatively simple structure. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel. [ABSTRACT FROM AUTHOR]

PN-sequence padding (PNP) TDS-OFDM transmission scheme has recently been proposed as an appealing alternative to the traditional Cyclic Prefix (CP) OFDM technology as it can provide significant improvement in the spectrum efficiency. In this paper, an iterative method is introduced to subtract the PN sequence. padding for the TDS-OFDM systems to mitigate the residual inter symbol interference (ISI) from the imperfect channel estimation, and the inherent channel estimation techniques are also performed to track the channel changes. Results show that this iterative algorithm can effectively remove the impact from the residual ISI on the slow-fading broadcast channels, even in the presence of very large channel delays in the single-frequency simulcast networks (SFN). [ABSTRACT FROM AUTHOR]