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
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