2 research outputs found
Toward Traffic Patterns in High-speed Railway Communication Systems: Power Allocation and Antenna Selection
In high-speed railway (HSR) communication systems, distributed antenna is
usually employed to support frequent handover and enhance the signal to noise
ratio to user equipments. In this case, dynamic time-domain power allocation
and antenna selection (PAWAS) could be jointly optimized to improve the system
performances. This paper consider this problem in such a simple way where
dynamic switching between multiple-input-multiple-output (MIMO) and
single-input-multiple-output (SIMO) is allowed and exclusively utilized, while
the channel states and traffic demand are taken into account. The channel
states includes sparse and rich scattering terrains, and the traffic patterns
includes delay-sensitive and delay-insensitive as well as hybrid. Some
important results are obtained in theory. In sparse scattering terrains, for
delay-sensitive traffic, the PAWAS can be viewed as the generalization of
channel-inversion associated with transmit antenna selection. On the contrary,
for delay-insensitive traffic, the power allocation with MIMO can be viewed as
channel-inversion, but with SIMO, it is traditional water-filling. For the
hybrid traffic, the PAWAS can be partitioned as delay-sensitive and
delay-insensitive parts by some specific strategies. In rich scattering
terrains, the corresponding PAWAS is derived by some amendments in sparse
scattering terrains and similar results are then presented.Comment: 30 pages, 9 figures, submitted for journal publicatio
Location-aware ICI Reduction in MIMO-OFDM Downlinks for High-speed Railway Communication Systems
High mobility may destroy the orthogonality of subcarriers in OFDM systems,
resulting in inter- carrier interference (ICI), which may greatly reduce the
service quantity of high-speed railway (HSR) wireless communications. This
paper focuses on ICI mitigation in the HSR downlinks with distributed transmit
antennas.For such a system, its key feature is that the ICIs are caused by
multiple carrier frequency offsets corresponding to multiple transmit antennas.
Meanwhile, the channel of HSR is fast time varying, which is another big
challenge in the system design. In order to get a good performance, low
complexity real-time ICI reduction is necessary. To this end, we first analyzed
the property of the ICI matrix in AWGN and Rician scenarios, respectively.
Then, we propose corresponding low complexity ICI reduction methods based on
location information. For evaluating the effectiveness of the proposed method,
the expectation and variance of remaining interference after ICI reduction is
analyzed with respect to Rician K-factor. In addition, the service quantity and
the bandwidth and computation cost are also discussed. Numerical results are
presented to verify our theoretical analysis and the effectiveness of proposed
ICI reduction methods. One important observation is that our proposed ICI
mitigation method can achieve almost the same service quantity with that
obtained on the case without ICI at 300km/h,that is, ICI has been completely
eliminated. Numerical results also show that the scenarios with Rician
K-factors over 30dB can be considered as AWGN scenarios, which may provide
valuable insights on future system designs.Comment: 30 pages, 6 figures, 3 table