Key focus: 5G NR resource block : a block of 14 OFDM symbols (1 slot across time domain) with the corresponding 12 subcarriers for those symbols
5G NR protocol stack
In the 5G New Radio (NR), the protocol architecture can be separated into two categories: user plane protocol stack and control plane protocol stack. The user plane protocol stack architecture is responsible for delivering user data and the control plane architecture is responsible for setting up the connection, maintaining mobility and providing end-to-end security.
The user plane protocol stack for 5G New Radio (NR) is shown in Figure 1. We see that at the physical layer interface (air interface) between the gNB and UE, the transmission occurs in the form of radio frames.
Radio frame structure
Looking at the 5G New Radio (NR) frame structure from the time domain perspective, the radio transmissions are categorized into radio frames, subframes, slots and mini-slots (Figure 2).
A radio frame is for a duration of 10 ms and it comprises of 10 subframes of duration 1 ms each. Each subframe may consist of one or multiple adjacent slots with each slot having 14 OFDM (Orthogonal Frequency Division Multiplexing) symbols. The possibility of transmission over a fraction of a slot is referred to as mini-slot.
Figure 1 shows the radio frame structure for the supported transmission numerologies (μ = 0, 1, 2, 3, 4) as per Table 1.
Because the duration of an OFDM signal is inversely proportional to its subcarrier spacing, the time duration of a slot scales with the selected numerology (Table 1).
From the frequency domain perspective, an OFDM symbol is comprised of 12 subcarriers, each subcarrier may be spaced according to the scalable numerology as per Table 1.
Time-Frequency resource
A resource element is the smallest time-frequency resource over one subcarrier of a single OFDM symbol. It is identified as (k,l)p,μ where k is the index of the subcarrier in the frequency domain, l is the OFDM symbol position in time domain, p is the antenna port and μ is the subcarrier spacing configuration defined in Table 1 above.
A resource block (a.k.a physical resource block – PRB) is a block of N RBsc = 12 subcarriers over which the transmissions are scheduled. 5G NR physical layer uses time-frequency resource (physical resource block) for transmission.
A resource grid consists of N size,μgrid,x subcarriers and N subframe,μ symb number of OFDM symbols (Table 2 and 3).
Hi, do not understand concept of data mapping onto subcarriers. Suppose simple scenario. We schedule PDSCH on some slot. As one RB is smallest allocation for UE, then will UE read 168 (14x12sc) or just 14(1sc) OFDM symbols of PDSCH data (suppose that we do nat have DMRS for PDSCH)? I guess the first case is valid, we still talk about TDD.
In 5G NR, a resource block (RB) is defined only for the frequency domain. i.e, a RB is a block of 12 subcarriers. We can assume that the minimum length of resource block is 1 OFDM symbol.
The exact Resource allocation for UE for PDSCH in time domain is defined by Start and Length Indicator Value (SLIV) or directly using the indicators : start symbol S and the allocation length L. Refer: ETSI TS 138 214 V17.3.0 (2022-09) section 5.1.2.1.
For Table 2 and Table 3, I believe the caption must read “slots per subframe” instead of “subframes per slot”
Thanks for pointing it out. It is now corrected.