In this paper, the downlink performance of OFDM and CDMA cellular systems is investigated for deployment scenarios similar to those envisioned by the 3GPP. In particular, the system-level performance characteristics a...
详细信息
In this paper, the downlink performance of OFDM and CDMA cellular systems is investigated for deployment scenarios similar to those envisioned by the 3GPP. In particular, the system-level performance characteristics are studied for packet data oriented systems with adaptive modulation and coding (AMC), operating on a 5 MHz channel with one-cell frequency reuse. For the CDMA case, both Rake and MMSE receivers are considered. Three link adaptation scenarios are considered: ideal (fast) time-only adaptation, slow link adaptation (based on average C/(I+N)), and ideal time-frequency adaptation (only for OFDM). Performance is evaluated using indicators such as total throughput and data rate profile, for five propagation environments (pedestrian A and B, Vehicular A and B, and GSM typical urban) and for single antenna systems as well as space-time transmit diversity (STTD) systems. Results show a significant performance benefit for fast link adaptation in all systems, and also indicate that OFDM provides a performance benefit that depends on the channel delay spread.
Adaptive modulation and coding (AMC) has gained a lot of attention in the research of high speed downlink packet access (HSDPA). The idea is to adapt the transmission to the fast changing channel conditions by the use...
详细信息
Adaptive modulation and coding (AMC) has gained a lot of attention in the research of high speed downlink packet access (HSDPA). The idea is to adapt the transmission to the fast changing channel conditions by the use of different modulation and coding schemes (MCS). In this paper, an adaptive algorithm (ITA) is presented for the AMC technique in HSDPA and a theoretical analysis model is introduced to investigate the throughput and FER of ITA. Subject to the given FER target, the numerical and link level simulation results both show that ITA outperforms the adaptive algorithms
In this report, a new technology of adaptive modulation and coding is proposed. This technique is designed for a cognitive radio system. The proposed technique is implemented into an ultra high speed wireless system. ...
详细信息
In this report, a new technology of adaptive modulation and coding is proposed. This technique is designed for a cognitive radio system. The proposed technique is implemented into an ultra high speed wireless system. The system has maximum 400 Mbps throughput with 80 MHz bandwidth. It is considered as an expanded model of the standard systems on IEEE 802.11a and 802.11n. When the throughput becomes high such as our designed wireless system, it is not easy to keep its throughput high enough under various circumstances. In order to obtain the optimum throughput under these circumstances, the proposed technique determines adaptively the specification of modulation and coding where several specifications of modulation can be designed and can be adaptively selected in our system. This report presents its evaluation of our proposed techniques. It is shown that the optimum condition is usually obtained in our system
High speed downlink packet access (HSDPA) is the packet-based data service with data transmissions up to 10 Mbps in WCDMA downlink. For HSDPA, adaptive modulation and coding (AMC) provides the flexibility to match the...
详细信息
ISBN:
(纸本)0780381149
High speed downlink packet access (HSDPA) is the packet-based data service with data transmissions up to 10 Mbps in WCDMA downlink. For HSDPA, adaptive modulation and coding (AMC) provides the flexibility to match the modulation and coding scheme to the average channel conditions for each user to raise the overall system capacity. There are many methods to estimate the channel quality, and the measurement of the mobile velocity is available for AMC. In this paper, the mobile velocity estimator using W-CDMA uplink signal for HSDPA is proposed. The proposed velocity estimator has robust pre-filter and post-filter to reduce noise influence. And the proposed velocity estimator also has observation block to estimate velocity more accurately under added noise.
We investigate the application of joint iterative decoding and channel estimation for the transmission of multilevel coded signals using asymmetric QPSK modulation over flat Rayleigh fading channels. The goal is the t...
详细信息
We investigate the application of joint iterative decoding and channel estimation for the transmission of multilevel coded signals using asymmetric QPSK modulation over flat Rayleigh fading channels. The goal is the transmission of multiresolution data streams to receivers with multi-level reception capabilities. We consider two types of receivers: the receivers in the first class can decode only the most significant bit (MSB) of the transmitted information; the receivers in the second class decode both the MSB and the LSB (least significant bit). Symbol aided demodulation (SAD) is used according to which known symbols are inserted in the encoded data stream to assist in the channel estimation process. Furthermore, an iterative algorithm is proposed that uses soft decoding information in addition to the information contained in the known symbols to improve the estimation of the fading channel. Simulation results show significant performance gains of the new scheme over both differential demodulation and conventional SAD.
M-ary phase shift-keying (MPSK) and M-ary frequency-shift-keying (MFSK) are compared for transmission over a Rayleigh faded radio channel of limited bandwidth. Both diversity and coding improvements are assessed for c...
详细信息
M-ary phase shift-keying (MPSK) and M-ary frequency-shift-keying (MFSK) are compared for transmission over a Rayleigh faded radio channel of limited bandwidth. Both diversity and coding improvements are assessed for coupling with the M-ary signal alphabet. It is shown that phase modulation, with coherent or differentially coherent detection, outperforms orthogonal MFSK signalling if both power and bandwidth are constrained. It is also shown that the use of lower-alphabet MFSK with a higher-order diversity is more advantageous than the use of higher-ary modulation. Some situations are exhibited in which a comparable performance can be obtained by an increase in signal alphabet or diversity; the choice of modulation and coding format depends on the relative complexity of higher-ary modulation compared to increasing the order of diversity.< >
Multi-carrier modulation techniques, such as OFDM, are attractive propositions for the design of future broadband wireless communication systems due to higher spectral efficiency than CDMA. A capacity enhancing techni...
详细信息
Multi-carrier modulation techniques, such as OFDM, are attractive propositions for the design of future broadband wireless communication systems due to higher spectral efficiency than CDMA. A capacity enhancing technique to be commonly used in these systems is adaptive modulation/coding (AMC) for link adaptation. With AMC, the modulation and coding scheme (MCS) is selected based on the channel quality information. MCS selection is an imperfect process by nature, due to, for example, the variability of the channel. Moreover, since the set of available MCSs is quantized, it is not always possible to select the optimal rate. Using these non-optimal MCS values results in reduced system capacity. This paper describes a method that attempts to maximize system and user throughputs in a multi-carrier system by overcoming the impacts of such non-optimal MCS selection through the use of hybrid ARQ (HARQ). This method relies on aggressive MCS selection and multiple HARQ transmissions. The performance impact of this method on various types of packet data applications is evaluated by system level simulation. Simulation results indicate that significant system and user throughput gains can be achieved by this method.
We develop an integrated subchannel scheduling algorithm to maximize the system throughput while guaranteeing minimum data rate requirements for multimedia users in multiuser MIMO-OFDM systems downlink transmission ut...
详细信息
We develop an integrated subchannel scheduling algorithm to maximize the system throughput while guaranteeing minimum data rate requirements for multimedia users in multiuser MIMO-OFDM systems downlink transmission utilizing adaptive modulation and coding (AMC) with limited channel state information feedback. By using the integrated subchannel scheduling, we apply the mathematical equivalence between antennas and subcarriers in the analysis, getting multiple parallel transmit subchannels, and then evaluating the channel state from the viewpoint of receivers. Joint space-frequency diversity as well as multiuser diversity is exploited simultaneously by the subchannel allocation algorithm. A modified proportional fair scheduling is proposed and a fast algorithm for more practical implementation is also proposed. By numerical examples, the system throughput and fairness superiority of our scheduling scheme are verified.
In this paper, adaptive modulation and coding structures are presented that are appropriate for the MUOS environment. The proposed approach adaptively controls the modulation format, FEC coding rate, transmission powe...
详细信息
In this paper, adaptive modulation and coding structures are presented that are appropriate for the MUOS environment. The proposed approach adaptively controls the modulation format, FEC coding rate, transmission power and even possibly bandwidth spreading gain in response to changing channel conditions in an attempt to optimize throughput while maintaining acceptable error rate performance. Being able to estimate and then predict the channel is vital to the system performance. Channel prediction algorithms; have been developed and the advantages of the adaptive modulation/coding techniques are presented together with implementation issues.
We propose an adaptive coding scheme that provides robust and spectrally-efficient transmission over strong atmospheric turbulence channels. We demonstrate that deep fades in the order of 35 dB and above can be tolera...
详细信息
We propose an adaptive coding scheme that provides robust and spectrally-efficient transmission over strong atmospheric turbulence channels. We demonstrate that deep fades in the order of 35 dB and above can be tolerated with proposed scheme.
暂无评论