FDD : Frame Structure Type 1
PCFICH(Physical Control Format Indicator Channel)
- It carries the number of symbols that can be used for control channels (PDCCH and PHICH).
- t is 16 data subcarriers of the first OFDM symbol of the subframe.
- The exact position of PCFICH is determined by cell ID and bandwidth.
PDCCH(Physical Downlink Control Channel)
- Mapped to the first L OFDM symbols in each of the downlink sub-frame.
- Number of the symbols (L) for PDCCH can be 1,2, or 3.
- Number of the symbols for PDCCH is specified by PCFICH
- PDCCH carries DCIs and the DCI carries Transport format, resource allocation, H-ARQ information related to DL-SCH, UL-SCH and PCH and other additional information depending on DCI format.
- PDCCH also carries DCI 0 which is for UL Scheduling assignment (e.g, UL Grants).
- Multiple PDCCH can be assigned in single subframe and a UE do blind decoding of all the PDCCHs.
- Carries H-ARQ Feedback for the received PUSCH
- After UE trasmitted the data in UL, it is waiting for PHICH for the ACK.
PDSCH(Physical Downlink Shared Channel)
- Carries user specific data (DL Payload).
- Carries Random Access Response Message.
- It carries the random access preamble
- It is occupying 72 subcarriers (6 RB) of bandwidth in the frequency domain.
P-SS(Primary Synchronization Signal)
- Mapped to 72 active sub carriers(6 resource blocks), centered around the DC subcarrier in slot 0 (Subframe 0) and slot 10 (Subframe 5).
S-SS(Secondary Synchronization Signal)
- Mapped to 72 active sub carriers(6 resource blocks), centered around the DC subcarrier in slot 0 (Subframe 0) and slot 10 (Subframe 5) in FDD.
RS (Reference Signal ) - Cell Specific
- These reference signal are carried by multiples of specific Resource Elements in each slots and the location of the resource elements are specifically determined by antenna configuration.
i) Time duration for one frame (One radio frame, One system frame) is 10 ms. This means that we have 100 radio frame per second.
ii) the number of samples in one frame (10 ms) is 307200 (307.200 K) samples. This means that the number of samples per second is 307200 x 100 = 30.72 M samples.
iii) Number of subframe in one frame is 10.
iv) Number of slots in one subframe is 2. This means that we have 20 slots within one frame.
< 36.211 Figure 4.1-1 : Frame Structure type 1 >
Now let's look at the basic units of horizontal axis which is time domain. The minimum unit of the time domain is a Symbol, which amounts to 66.7 us. Regardless of bandwidth, the symbol length does not changes.In case of time domain, we have a couple of other structures as well. The largest unit in time domain is a frame, each of which is 10 ms in length. Each of the frame consists of 10 sub frames, each of which is 1 ms in length. Each of sub frame consists of 2 slots, each of which is 0.5 ms in length.Each of slots consists of 7 symbols, each of which is 66.7 us.
With this in mind, let's think about the scale in reverse direction.
Q> How many symbols are there in a slot ? A> 7 symbols.
Q> How many symbols in a sub frame ? A> 14 symbols.
Q> How many slots are there in a frame ? A> 20 slots.
Now let's look at the units which is made up of both time domain (horizontal axis) and frequency domain (vertical axis). Let's call this type of unit a two-dimensional unit.
The minimum two dimensional unit is resource element which is made up of one symbol in time domain and one sub carrier in frequency domain. Another two dimensional unit is resource block(RB) which is made up of one slot in time domain and 12 sub-carrier in frequency domain. Resource Block(RB) is the most important units in LTE both for protocol side and RF measurement side.
Now here goes questions.
Q> How many symbols in a resource block ? A> 7 symbols.
Q> How many sub-carriers in a resource block ? A> 12 sub-carriers.
Q> How many resource elements in a resource block ? A> 84 resource elements.
Now it's time to combine all the units we covered. The following questions are very important to read any of the LTE specification.
Q> How many resource blocks in a 20 Mhz band ? A> 100 resource blocks.
Q> How many resource blocks in a 10 Mhz band ? A> 50 resource blocks.
Q> How many resource blocks in a 5 Mhz band ? A> 25 resource blocks.