03 01 RA41203EN60GLA0 Air Interface

LTE FDD Air Interface

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The Guard Period should be designed such that it is always longer than the multipath delay spread, in order to avoid inter-symbol interference between successive OFDM symbols. Note that in the example of this slide, the Guard Period is too short, so there will be inter-symbol interference!


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•The OFDM signal is made of multiple subcarriers.

•The distance between the center frequencies of the subcarriers is exactly the inverse of the Symbol period (Ts). Bigger Ts means subcarriers will allocated closer and more subcarriers could be allocated on a given spectrum bandwidth.

•An OFDM symbol is the combination of “n” subcarrier Symbol being produced in parallel at the same time.


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Fixed 15kHz: reduces the complexity of a system supporting multiple channel bandwidths

MBMS: Multimedia Broadcast Multicast system

To ensure that all signals are received correctly, the receiver sampling rate must be slightly higher than the bandwidth of the signal used to carry it (i.e. for a channel bandwidth of 1.75MHz the sampling rate should be 2 MHz)


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• Reference signals position in time domain is fixed (symbol 0 & 4 / slot for Type 1 Frame) whereas in frequency domain it depends on the Cell ID

• Reference signals are modulated to identify the cell to which they belong.

• This signal, consisting of a known pseudorandom sequence, is required for channel estimation in the UEs..

• Note that in the case of MIMO transmission, additional reference signals must be embedded into the resource blocks.


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Principle of OTDOA:

Special signals in RL: PRS (Positioning Reference Signals)

With the PRS from different eNBs the UE determines the 3 unknowns (x, y and absolute time) *)

UE is informed about PRS configuration by the LPP (LTE Positioning Protocol) defined between UE and E-SMLC

LPP is used to transport the OTDOA measurements called RSTD (reference signal time difference) from UE to E-SMLC

LPP protocol entities are transparent to eNB

Computation of UE position from RSTD measurements is done by E-SMLC (Remark: not covered by this feature)

Prerequisite : Cells transmitting PRS must have a synchronous air interface *) At least PRS from 3 eNB are required, however in some cases it might be that with 3 eNB no unique solution exists. With PRS from 4 eNB this un-ambiguity is removed.


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he first steps after switching on the mobile are the following:

1. Primary Synchronization Signal PSS– from which the mobile can acquire frequency and time-slot synchronization. The synchronization is absolutely necessary, otherwise the mobile cannot read the rest of the physical channels. Also from the PSS the mobile is learning the cell identity – which could have values 0,1 or 2 in LTE. The cell identities are used to differentiate between different cells

2. Secondary Synchronizations Signal SSS – from which the mobile can learn what is the frame structure (10 ms in LTE). Also the physical cell id group with values from 1 to 168 is achieved. The physical cell id together with the group are used to separate the cells in LTE.

3. DL reference signals – they have almost the same functionality like the CPICH (common pilot channel) in UMTS. Used for channel estimation and measurements. Details of the measurements are provided in chapter 8.

4. PBCH – Physical Broadcast Channel. From this channel the UE is learning about the system information. Please note that in LTE the PBCH is designed to have minimum possible information (for coverage reasons mainly). Therefore the rest of system information which is organized in MIB = Master information Block and SIBs = System Information Blocks is now sent on the Physical Downlink Shared Channel PDSCH. From PBCH the UE is learning the system bandwidth 1.4, 3, … 20 MHz and the PHICH = Physical HARQ Indication Channel configuration.


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Because the SIBs are placed on the PDSCH then the mobile should now read the PDSCH. The steps are the following:

5. PCFICH (Physical Control Format Indicator Channel) indicates how many symbols in the beginning of each subframe (1 subframe is having 1 ms in LTE) are allocated for the PDCCH. This is beacuse the size of the PDCCH may be changed based on several variables like cell bandwidth, cell load ...

6. PDCCH (Physical Downlink Control Channel) – from this channel the mobile can learn: what are the physical resources allocated for the mobile and where are they placed in the time and frequency

7. Finally the UE may read the PDSCH to read the MIB and the SIBs. For a detailed list of SIBs please refer to the section Downlink Transmission

After the mobile is reading the system information from the PDSCH the next step is the so called cell selection and reselection. The basic idea is that the UE is measuring several cells and is selecting the best one with the help of the thresholds from the system information


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For the initial random access the steps are the following

8A – the mobile is selecting randomly one preamble. There are in total 64 preambles available in one cell. In this case with A it is intended to note the first random preamble

8C – If no answer is received from the eNode B then the mobile will repeat the preamble. In this example C is the 3rd preamble. That means after three preambles the UE receives an answer from the Node-B


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In the next step the UE should receive the answer to the preamble. However, the answer is sent on the PDSCH. Therefore the steps are as follows:

9. PCFICH (Physical Control Format Indicator Channel) indicates how many symbols in the beginning of each subframe (1 subframe is having 1 ms in LTE) are allocated for the PDCCH. This is because the size of the PDCCH may be changed based on several variables like cell bandwidth, cell load ...

10. PDCCH (Physical Downlink Control Channel) – from this channel the UE can learn: what are the physical resources allocated for the UE and where are they placed in the time and frequency

11. PDSCH – containing the random access response. In this message the id of the transmitted preamble should be included. Also the eNode-B allocates to the UE the C-RNTI = Cell Radio Network temporary Identity. C-RNTI is allocated by the eNB serving a UE when it is in active mode (RRC_CONNECTED). This is a temporary identity for the user only valid within the serving cell of the UE. It is exclusively used for radio management procedures.


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Please note how the contention resolution is done:

If several UEs are in contention then they all receive the same UL grant from the eNodeB. So the RRC Connection Request (sent on Uplink PUSCH) message is sent with high probability of error.

If the eNode-B cannot decode the RRC (because of high interference), then all the UEs involved in the collision will restart the random access (restart from message 8A).

If the eNode-B detects the message of at least one UE, it then sends the answer with the identity of this UE. All the other UEs involved in the collision do not receive an answer specific to them, will restart the initial access.

The message flow is as following:

11. PDSCH – containing the random access response. In this message the id of the transmitted preamble should be included. Also the eNode-B allocates to the UE the C-RNTI = Cell Radio Network temporary Identity. Also very important – this message is containing the UL grant, that is, indicating to the UE what are the resources that the UE could use in the UL for PUSCH (Physical UL Shared Channel)

12. PUSCH Physical UL Shared Channel. The UE sends the higher layer message – RRC Connection Request. The message can include the C-RNTI allocated in 11 and also the NAS ID.

13. PDSCH – contention resolution message. As explained this message is only sent if the eNode-B could decode the message number 12 from the UE. The message should contain the UEID such as the C RNTI or NAS ID.


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The message flow for the DL transmission is as following (please note that for simplicity the notation of the messages counter is restarted from 1).

1. DL reference Signals - Used for channel estimation and measurements.

2. PUCCH – used in this in scenario to indicate the CQI based on the measurements performed in the previous step. Please note that PUCCH or PUSCH could be used depending on whether the UE is allocated UL for data transmission or not.

3. PCFICH indicates how many symbols in the beginning of each subframe (1 subframe is having 1 ms in LTE) are allocated for the PDCCH. This is because the size of the PDCCH may be changed based on several variables like cell bandwidth, cell load ...

4. PDCCH (Physical Downlink Control Channel) – from this channel the UE can learn: what are the physical resources allocated for the UE and where are they placed in the time and frequency. Also the modulation and coding scheme should be indicated.

5. PDSCH – data transmission (this is the web page from the Internet).

6. ACK or NACK for the user data on 5. This is for HARQ retransmission .

7. In Case of NACK then the user data sent 5 has to be retransmitted .


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The message flow for the UL transmission is as follows:

1.PUCCH – the UE is requesting the eNode-B to schedule some physical

resources for the UL transmission. Please note that the eNode-B is in charge of

the UL scheduling also. Also note that the scheduling request is only needed for

applications without semi persistent scheduling, (not currently supported in

Nokia)

2. UL sounding reference signal – used for the channel dependent scheduling.

3. UL Demodulation Signal. Used for channel estimation reasons.

4. PDCCH – used in this scenario to indicate the UL grant, that is, what are the

physical resources which could be used by the mobile for the UL transmission

5.PUSCH – this is the actual user data transmission.

6.PHICH – this is actually on DL channel on which the ACK or NACK for the

HARQ are transmitted.

7.PUSCH – retransmission of user data if 6 is indicating NACK .


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List of detected preambles: The eNB shall report a list of detected PRACH preambles to higher layers. Higher layer utilize this info for the RACH procedure

Transport BLER: The ACK/ NACKs for each transmission of the HARQ process are reported to the MAC. Based on these ACK/NACKs the higher layers compute the BLER for RRM issues.

TA: The eNB needs to measure the initial timing advance (TA) of the uplink channels based on the RACH preamble

Average RSSI: Measured in UL by eNB. It can be used as a level indicator for the UL power control. The RSSI measurements are all UE related and shall be separately performed for ( TTI intervals)

· UL data allocation (PUSCH)

· UL control channel (PUCCH)

• Sounding reference signal (SRS)

Average SINR: In UL the eNB measures SINR per UE. The average SINR can be used as a quality indicator for the UL power control

UL CSI: channel state information per PRB for each UE. The CSI shall be the received signal power averaged per PRB.


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CSPs can use their existing mobile softswitching and Nokia Solutions Networks’ Mobile VoIP Server (NVS) infrastructure to manage voice traffic over the LTE network, a function that will eventually be handled by IP Multimedia Subsystem (IMS). This gives CSPs an important time-to-market advantage.

Fast Track VoLTE provides a transitional step between traditional networks and the all-IP world of LTE. The solution allows CSPs to exploit their existing circuit-switched mobile core network investments, while providing next-generation service. Investments in Fast Track VoLTE are fully re-usable when upgrading network architecture to IMS, thus reducing capital expenditure (CAPEX) in the long term.

NVS: if MSC, NVS is provided by a SW upgrade and a minor HW addition.


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03 01 RA41203EN60GLA0 Air Interface

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