Digital Signal Processing Reference
In-Depth Information
Fig. 2.3
Flexible resource
allocation in time and
frequency for LTE
the run time. Finally, handover between cells is briefly summarized, which is an
additional flexibility present in current wireless networks.
LTE uses a time-frequency-space grid to allocate resources to users in the DL
and in the UL (Fig.
2.3
). Users are allocated a certain number of resource blocks
consisting of 12 consecutive subcarriers during a time slot of 0.5 ms. In the time
domain, DL and UL transmissions are organized in radio frames of 10 ms, both for
TDD and FDD.
The same coding and modulation is applied to all groups of resource blocks be-
longing to the same L2 PDU (packets at MAC level) scheduled to one user within
one TTI (subframe) and within a single stream. Therefore, the smallest granularity
for assigning different modulations or profiles is 12 consecutive subcarriers during
a 1 ms period.
In total, each resource block (PRB) consists of 84 resource elements (12 sub-
carriers during 7 OFDM symbols). However, some of the resource elements within
a resource block will not be available as they are already occupied for reference
signals or control information.
Even though a downlink resource block is defined in terms of PRBs the downlink
resource block assignment is carried out in terms of pairs of PRBs, where each pair
