Digital Signal Processing Reference
In-Depth Information
LTE networks. In [27] this Self-X technology is used for the self-configuration of
fractional frequency reuse for LTE that uses only local information. Their solution
achieves a trade-off between locality of the information, optimality and stability of
the solution. This trend to move from design time planning of the network towards
self-configuration during the run time, taking into account specific information that
can only be obtained during the run time, is the basis of the design methods proposed
in this topic.
2.2.2.3 LTE-Advanced
LTE advanced is the push towards 4G wireless technologies. It aims to even further
data rates than LTE [24] in line with 4G requirements. The most important require-
ment is the very high data rate, which is 100 Mbps for high mobility and as high as
1 Gbps for low mobility. This low mobility mode is the focus, since LTE advanced
mainly aims at achieving high data rates. However, mobility support across the cel-
lular network up to 350 km/h (even up to 500 km/h depending on the frequency
band) is also included.
To achieve 1 Gbps, the bandwidth is increased up to 100 MHz. For backwards
compatibility with LTE, this is implemented by aggregating up to 5 carriers with a
bandwidth of 20 MHz. In addition, the number of spatial streams is increased up to
8
×
×
4 for UL. Next to SDM, the MIMO modes include beamform-
ing to improve the performance at the cell edges. For this, multi-cell beamforming
is also possible, which means that multiple eNB's cooperate to transmit data to a
cell edge user. In addition to cooperative multipoint transmissions, cell edge per-
formance can be improved by means of relaying. Both layer 1 and layer 3 relaying
is considered. The target spectrum efficiency is 30 bps/Hz for the downlink and
15 bps/Hz for the uplink. Finally, the number of active users that should be sup-
portedina5MHzband is increased to 300.
To make optimum use of all the possible frequency bands, and with a flexible
bandwidth up to 100 MHz, it is clear that the frequency planning and configuration
is even more flexible than for LTE. In addition to that, with relaying and multi-cell
beamforming, the number of possible transmission modes is increased dramatically.
As a result, the trend towards self-configuration and self-optimization is supported
even more for LTE-advanced. Both flexible spectrum usage and more Self-X are
important features of cognitive radio networking.
8 for DL and 4
2.3 Spectrum Access Flexibility
Spectrum is becoming a major resource constraint when designing radio systems.
The accelerated deployment of broadband personal communication coupled with
the continuously increasing demand for large data rates results in an increasing spec-
trum scarcity. Wireless technology on the other hand is becoming more and more
