LTE Resource Allocation Tool

 

LTE provides huge flexibility when it comes to allocation of downlink and uplink resources on the air interface. The LTE resource allocation tool supports you in your everyday LTE work and helps you to understand some basic parameters related to scheduling and resource allocation as defined in 3GPP specifications TS 36.211 to 36.213.

 

The tool consists of seven modules:

The modules "Resource Allocation Type 2 Downlink" and "Resource Allocation Type 2 Uplink" assist you in interpreting the important case of resource allocation type 2. Based on the number of LTE resource blocks you want to allocate and the starting resource block in the frequency domain, the resource indication value (RIV) is calculated (RB to RIV). The RIV is used for signaling the resource allocation from the base station to the terminal. The other way round also works: A given RIV can be converted to the corresponding number of resource blocks and starting resource block (RIV to RB). The resulting resource allocation is graphically displayed. Please note that localized resource allocation is assumed for downlink.

The modules "Transport Block Size Downlink" and "Transport Block Size Uplink" evaluate the transport block sizes and modulation and coding schemes (MCS) that can be carried over a given resource allocation. Enter a combination of resource block allocation size and MCS value, and the resulting transport block size, code rate and modulation scheme will be displayed.

The module "Search Space" calculates the UE-specific search space for a given combination of channel bandwidth, frame structure type, number of antennas, number of symbols in PDCCH and the scaling factor Ng. For frame structure type TDD the uplink-downlink configuration and subframe number are also required. A table will be displayed showing the UE-specific search space for all aggregation levels, transmission time intervals (TTI) and PDCCH candidates.

The module "UCI over PUSCH" calculates the impact of uplink control information (UCI) on the code rate of the PUSCH. Based on the input of some parameters about the PUSCH and the UCI configuration, the module calculates the effective code rate with UCI as well as the separate code rates of the CQI and the HARQ Ack/Nack bits.

 

A brief explanation of some of the terms used is given below. For a detailed explanation, please refer to www.rohde-schwarz.com/appnote/1MA111.

 

Resource block (RB): The basic LTE resource entity in the frequency domain is the resource block of 180 kHz. One or more resource blocks can be allocated to a terminal for data transmission and reception. LTE supports scalable bandwidths from 1.4 MHz up to 20 MHz, corresponding to different numbers of resource blocks (6 up to 100) that can be allocated at maximum.

 

Resource Allocation Type: For efficient signaling of the resource allocations from the base station to the terminal, different resource allocation types are supported. In resource allocation type 2, which is used in downlink and uplink, a starting resource block and an allocated number of resource blocks are signaled to the terminal. In order to save signaling bits on the downlink control channel (physical downlink control channel, PDCCH), these two parameters are not explicitly signaled. Instead, a resource indication value (RIV) is derived which is signaled in downlink control information on PDCCH.

 

Transport block: Higher layer data packets are multiplexed onto transport blocks which are delivered to LTE physical layer for transmission. Per LTE transmission time interval of 1 ms, one transport block (or up to two in the case of MIMO spatial multiplexing) can be transmitted.

 

Modulation and coding scheme (MCS): The MCS index (0 ... 31) is used by the base station to signal to the terminal the modulation and coding scheme to use for receiving or transmitting a certain transport block. Each MCS index stands for a certain modulation order and transport block size index. The latter can be used to derive the transport block size for a given resource block allocation.

 

Code rate: The code rate is defined as the ratio between the transport block size and the total number of physical layer bits per subframe that are available for transmission of that transport block. The code rate is an indication for the redundancy that has been added due to the channel coding process. In the Transport Block Size modules, the calculation of the code rate in downlink assumes SISO (single input single output) operation and does not take into account the Physical Broadcast Channel (PBCH) and Synchronization Channels (P/S-SCH). For uplink, sounding reference signal (SRS) overhead is not considered.