OFDMA Parameter for LTE
- How Many OFDMA Parameter for LTE?
- Which is OFDMA Parameter for LTE ?
The width of a Sub-carrier is 15 kHz whatever the bandwidth
- The bandwidths are: 1.4, 3, 5, 10, 15 and 20 MHz
- Note that in LA1.1, only 5, 10 MHz are implemented
The symbol duration is always the same whatever the bandwidth
- There are 2 times more sub-carriers in 10 MHz than in 5 MHz
- 2 times more symbols can be sent or received at the same time.
- The capacity is multiplied by 2
Reduced subcarrier spacing of 7.5 KHz for MBSFN operation also supported
• Center subcarrier (DC subcarrier) not used to allow for direct conversion receiver implementation
- For the 5 MHz, there are 512 sub-carriers of 15 kHz. The total band is 7.68 MHz. It is larger than the 5 MHz band!
- But only 301 sub-carriers are used (Pilot, DC, data), the other ones are guard sub-carriers: 301 Sub-ca * 15 kHz = 4.515 MHz
Flexible bandwidth allocation supported by OFDM
• Still different RF filter will be required
• Frame structure always the same
• Sampling frequency is an transmitter and receiver implementation issue
• Sampling rate is multiple of 3.84 MHz ? single clock for multi-mode UE with WCDMA
• Smallest bandwidth that is supported was modified recently and needs to be updated The symbol duration depends on the sub-carrier width.
2 Cyclic Prefixes are defined by the 3GPP:
- Long CP: 16.67 micro seconds
- Normal CP: 4.69 micro seconds
- Only the normal CP is supported in LA1.x
- The total duration of a symbol is: Useful duration + CP = 66.6 + 4.69
- Total duration = 71.29
OFDMA Parameters for LTE
OFDMA in LTE relies on several key parameters to efficiently manage data transmission. I’d start with the most important one: the subcarrier spacing. In LTE, the subcarrier spacing is set to 15 kHz, which is optimized for high data rates and effective spectral efficiency. This spacing allows the system to send multiple data streams simultaneously without interference.
Another key parameter is the number of subcarriers. In the LTE downlink, the number of subcarriers is determined by the bandwidth allocation. For example, in a 20 MHz channel, you’ll have 1,200 subcarriers available. I’d say this scalability allows LTE to handle different channel widths effectively, ranging from 1.4 MHz to 20 MHz.
Additionally, the FFT size is an important parameter. It’s typically set to 2048, which helps the system divide the spectrum into smaller chunks, making it easier to allocate resources. The length of the cyclic prefix is another factor to consider; LTE uses both normal and extended cyclic prefixes, which help mitigate multipath interference by providing a buffer zone in the signal.
All these parameters work together to ensure that LTE can provide fast, reliable data transmission, whether you’re in a dense urban area or on the outskirts of the network.