1 research outputs found
Multi-User Scheduling in the 3GPP LTE Cellular Uplink
In this paper, we consider resource allocation in the 3GPP Long Term
Evolution (LTE) cellular uplink, which will be the most widely deployed next
generation cellular uplink. The key features of the 3GPP LTE uplink (UL) are
that it is based on a modified form of the orthogonal frequency division
multiplexing based multiple access (OFDMA) which enables channel dependent
frequency selective scheduling, and that it allows for multi-user (MU)
scheduling wherein multiple users can be assigned the same time-frequency
resource. In addition to the considerable spectral efficiency improvements that
are possible by exploiting these two features, the LTE UL allows for transmit
antenna selection together with the possibility to employ advanced receivers at
the base-station, which promise further gains. However, several practical
constraints that seek to maintain a low signaling overhead, are also imposed.
In this paper, we show that the resulting resource allocation problem is
APX-hard and then propose a local ratio test (LRT) based constant-factor
polynomial-time approximation algorithm. We then propose two enhancements to
this algorithm as well as a sequential LRT based MU scheduling algorithm that
offers a constant-factor approximation and is another useful choice in the
complexity versus performance tradeoff. Further, user pre-selection, wherein a
smaller pool of good users is pre-selected and a sophisticated scheduling
algorithm is then employed on the selected pool, is also examined. We suggest
several such user pre-selection algorithms, some of which are shown to offer
constant-factor approximations to the pre-selection problem. Detailed
evaluations reveal that the proposed algorithms and their enhancements offer
significant gains.Comment: To appear, IEEE Transactions on Mobile Computin