difference between NB-IOT and LTE in RACH

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difference between NB-IOT and LTE in RACH

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Hi.

LTE RACH procedure include 4 steps. In 1st step UE sends preamble to eNB. UE use 6 RB for sending preamble.

In NB-IoT same 4 steps exist. But I do not know how many RBs are needs for sending preamble.

Also I read it is hierarchical and it depend on repetition level. what is repetition level? 

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I want to know about difference between LTE-A and NB-IoT. I say welcome for explain or introduce good documentSmile

Thanks.

All Replies
  • NB-IoT has 6 RBs for sending preambles. In the frequency range, subcarrier spacing of 3.75 kHz is applied. NPRACH resources occupy a contiguous set of either 12, 24, 36 or 48 subcarriers and are located on a discrete set of subcarrier ranges. The preamble is based on symbol groups on a single subcarrier. Each symbol group has a cyclic prefix (CP) followed by 5 symbols. Two preamble formats are defined, format 0 and format 1, which differ in their CP

    length. The five symbols have a duration of 1.333 ms, prepended with a CP of  67 μs for format 0 and 267 μs for format 1, giving a total length of 1.4 ms and 1.6 ms, respectively. The preamble format to be used is broadcasted in the system information.The preamble is composed of 4 symbol groups transmitted without gaps. Frequency hopping is applied on symbol group granularity, i.e. each symbol group is transmitted on a different subcarrier. By construction, this hopping is restricted to a contiguous set of 12 subcarrier. Depending on the coverage level, the cell may indicate that the UE shall repeat the preamble 1, 2, 4, 8, 16, 32, 64, or 128 times, using the same transmission power on each repetition.

  • J.Y.Lee

    NB-IoT has 6 RBs for sending preambles. In the frequency range, subcarrier spacing of 3.75 kHz is applied. NPRACH resources occupy a contiguous set of either 12, 24, 36 or 48 subcarriers and are located on a discrete set of subcarrier ranges. The preamble is based on symbol groups on a single subcarrier. Each symbol group has a cyclic prefix (CP) followed by 5 symbols. Two preamble formats are defined, format 0 and format 1, which differ in their CP

    length. The five symbols have a duration of 1.333 ms, prepended with a CP of  67 μs for format 0 and 267 μs for format 1, giving a total length of 1.4 ms and 1.6 ms, respectively. The preamble format to be used is broadcasted in the system information.The preamble is composed of 4 symbol groups transmitted without gaps. Frequency hopping is applied on symbol group granularity, i.e. each symbol group is transmitted on a different subcarrier. By construction, this hopping is restricted to a contiguous set of 12 subcarrier. Depending on the coverage level, the cell may indicate that the UE shall repeat the preamble 1, 2, 4, 8, 16, 32, 64, or 128 times, using the same transmission power on each repetition.

    Thanks J.Y.Lee

    I want to know about RACH procedure. I do not know simple concept. For example:

    1. I heard about CE level and repetition level in RACH procedure. What means of this levels for accessing to network?

    2. NB-IOT use eMTC preamble. What means of this?

    3. Are the preambles for normal users and preambles for NB-IoT different? How can we divide them?

    4. How the RACH procedure is improved in NB-IoT vs normal LTE?

    5. I can not find out this sentence "the cell may indicate that the UE shall repeat the preamble 1, 2, 4, 8, 16, 32, 64, or 128 times, using the same transmission power on each repetition". Can you explain more?

    Thank you

  • 1. According to the 3GPP specification [TS 36.213], cells classify the UEs into three coverage-enhancement (CE) levels depending on the radio condition. Each CE level has PRACH resources.

    2. Umm.... I don't understand your question exactly. Unlike the LTE system, in NB-IoT, preamble is not composed of  codes (e.g., zad-off chu), just frequency hopping based method that occupy a certain frequency band.

    4. The two systems (LTE, NB-IoT) have simillar RACH procedure. But, there are some differences between them.

    First, preamble formant is different. LTE has code based preamble, but NB-IoT's preamble is just subcarrier. Second, NB-IoT is based on CE level. Thus, PRACH resource is allocated to each CE level. Third, NB-IoT depends on random access procedure for transmitting data. In contrast to LTE networks, the NB-IoT does not have dedicated radio resources for scheduling requests.

    5. In NB-IoT, preamble is repeatedly transmitted. 1,2,..., 128 is the number of repeatition. A certain repeatition number is selected according to CE level.