What is the difference between 5g and 4g

I. Comparison of frame structure

1.4G and 5G similarities

Frame and sub-frame lengths are: 10ms and 1ms.

Minimum scheduling unit resource: RB

2.4G and 5G differences

1); Sub-carrier width

4G: Fixed at 15kHz.

5G: Multiple options, 15kHz, 30kHz, 60kHz, 120kHz, 240kHz, and multiple subcarrier bandwidths can be transmitted simultaneously in a 5G frame.

2); Minimum scheduling unit time

4G: TTI, 1 millisecond;

5G: slot , 1/32 millisecond~1 millisecond depending on subcarrier bandwidth.

Additionally 5G adds mini-slot, which takes up a minimum of only 2 symbols.

3); Number of time slots (symbols) per subframe

4G: 2 time slots per subframe, normal CP, 7 symbols per time slot.

5G: 1-32 time slots per subframe depending on subcarrier bandwidth, normal CP with 14 symbols per time slot.

4G scheduling unit is subframe (ordinary CP contains 14 symbols); 5G scheduling unit is time slot (ordinary CP contains 14 symbols).

3.5G design concept analysis

1); time-frequency relationship

Basic principle: the subcarrier width and symbol length is an inverse relationship between the subcarrier width and the symbol length, wide subcarriers short symbols, narrow subcarriers long symbols;

Performance: the total bandwidth is fixed, the number of time-frequency 2D composition of the RE resource is fixed, does not change with the subcarrier bandwidth, the throughput is also the same.

2); Reduced delay

Selecting wide subcarriers, the symbol length becomes shorter, while 5G scheduling is fixed to 1 time slot (12/14 symbols), the scheduling delay becomes shorter.

When selecting the maximum subcarrier bandwidth, single scheduling is reduced from 1 ms (15 kHz) to 1/32 ms (480 kHz), which is more favorable for URLLC services.

4. 5G subcarrier bandwidth comparison

1); Coverage: narrow subcarrier is good

Services, public **** channel: small subcarrier bandwidth, symbol length is long, the length of the CP is sung, and resistance to inter-symbol interference brought about by multipath is strong.

Public **** channel: for example, PUCCH, PRACH need to be uploaded in a RB finished, small subcarrier per RB bandwidth is also small, high uplink power density.

2); overhead: narrow subcarriers are good

Scheduling overhead: for large carrier bandwidth, there will be more slot units to be scheduled in each frame, scheduling overhead increases.

3); delay: wide subcarrier is good

Minimum scheduling delay: large subcarrier bandwidth, symbol length is small, the minimum scheduling unit slot occupies a short period of time, the shortest 1/32 milliseconds.

4); mobility: wide subcarrier is good

Doppler frequency shift tolerance: in the frequency shift must be the case, the influence of large bandwidth is small, the inter-subcarrier interference is small.

5); processing complexity: wide subcarrier good

FFT processing complexity: for example, 15kHz, better than FFT more, the device can only support to 275 RB (50MKz).

5.5G common subcarrier bandwidth

1); C-Band

eMBB: 30kHz is currently recommended.

URLLC: wide subcarrier bandwidth.

6. Self-contained

4G: single subframe is either downlink only or uplink only (except for special subframes), uplink subframes are transmitted after downlink subframes have been transmitted, and with a 3:1 ratio, downlink transmission starts 3ms before uplink feedback starts, which results in higher latency.

5G: Inside each time slot, the control channel is introduced in the opposite direction to the direction of the digital transmission, which can achieve fast feedback to reduce (downlink feedback delay and uplink scheduling delay), for example, at 30kHz, the feedback can be done in units of 0.5ms, and with other large subcarrier bandwidths, a much smaller latency can be achieved.

TDD uplink and downlink ratios

1. TDD analysis

1) Advantage

Resource adaptation: adjust uplink and downlink resource ratios in accordance with network demand.

Better support for BF: upstream and downstream same-frequency mutual anisotropy, better support for BF.

2), Disadvantages

Requires GPS synchronization: requires strict time synchronization.

Overhead: upstream/downstream conversion requires a GAP, waste of resources.

Interference: prone to inter-station interference, such as TDD ratio misalignment, ultra-far interference.

2. 5G from TDD-LTE

No innovation in TDD ratio: LTE and 5G are similar in TDD ratio design, with adjustable upstream and downstream ratio.

Dynamic TDD for a short time is unlikely: there can only be one TDD ratio for the same network, otherwise there is serious inter-base station interference.

TDD ratios will converge: from LTE, a lot of TDD ratios were defined in the early days, but they eventually converged to a 3:1 ratio (downlink to uplink resources), and this should be the case for 5G as well.

Synchronization: synchronization between 5G operators, synchronization between NR and TDD-LTE.

3. Channel: transmitting high-level information

1. Public **** channel

1); downlink

a) PCFICH,PHICH

4G: has this channel.

5G: this channel is removed, reducing the latency requirement.

b)PDCCH

4G: no proprietary demodulation guide, no BF support, no support for multiuser multiplexing, poor coverage and capacity; PDCCH is hashed in the frequency domain, with frequency-selective gain, but forward compatibility is bad, e.g., GL dynamic **** enjoyment, need to consider how to circumvent PDCCH.

5G: has proprietary demodulation guide frequency (DMR), supports BF, supports multi-user multiplexing, good coverage (9db gain) and capacity; PDCCH is set in a specific location, forward compatibility, want to take some of these bands out is simple.

c)Broadcast channel

4G: frequency domain location is fixed, placed in the center of the bandwidth, does not support BF.

5G: location is flexible and assignable, forward compatibility is strong, BF is supported, and the coverage is improved by 9db.

2)Uplink

a) PUCCH

4G: scheduling the smallest unit, RB.

5G: scheduling minimum unit symbol, can be placed in special subframes.

2. Service **** channel

1)Downlink PDSCH

4G: no proprietary guide frequency except LTE MM, up to 64QAM modulation.

5G: with proprietary guide frequency, up to 256QAM modulation, 33% efficiency improvement.

2)Uplink PUSCH

4G: up to 64QAM modulation.

5G: up to 256QAM modulation, 33% efficiency improvement.

4. Signal: auxiliary transmission, no high-level information

1. Signal type

4G: Measurement and demodulation are used *** with the CRS (measurement of RSRP PMI RI. CQI measurement of the phase to demodulation), of course, LTE MM (MM: Massive Mimo, multi-antenna technology, the same below) has a proprietary guide frequency and CRS *** enjoy.

5G: remove CRS, add CRI-RS (measuring RSRP PMI RI CQI), and support BF; new DMRS demodulation dedicated DMRS (measuring phase demodulation) and support for BF, all channels have a proprietary DMRS, 12 ports of DMRS plus spatial multiplexing to support up to 32 streams.

2. Comparison

1); Coverage

4G: CRS without BF, RSRP poor.

5G: CRI-RS has BF (BF: Beam Forming, beam fouling, same below), 9db coverage gain (10*log (8 column array)) compared to LTE RSRP.

2); light load interference

4G: light load interference is big. No BF, interference is a little bigger; momentary sending, even if no-load is sent throughout the small area, there is interference to the neighboring area; small inter-area staggered sending, even if no-load countless passes the neighboring area's data to the interference.

5G: BF and narrow-band scanning, interference is smaller; can only send a certain sub-band, neighboring interference is small, countless passes of the sub-band will not interfere with the neighboring area; neighboring inter-area position is not bad open, no data RE interference to the neighboring area.

3); capacity

a); guide frequency overhead: almost

4G: CRS in each RB accounted for 16 RE, if MM then there are proprietary guide frequency RE 12.

5G: 2 to 4 REs per RB for CSI-RS and 12 to 24 REs for DMRS.

b); Single-user capacity

4G: The protocol defines 2 ports for DMRS, so a maximum of 2 streams for a single user at MM.

5G: The protocol defines a 12-port DMRS, and a single user can support up to 8 streams as specified in the protocol, but of course the implementation is estimated to be up to 4 streams considering the size limitation of the terminal.

V. Multiple Access

1. 9% peak enhancement

4G: OFDM bandwidth utilization of 90%, the left and right each leave 5% of the band mess as a protection band.

5G: F-OFDM bandwidth utilization 98.3% (filter reduces protection band).

2. 30% average uplink improvement

4G: Single carrier technology is used for uplink. Advantage: because of low PAPR, high transmit power, good coverage at the edge; Disadvantage: because it is a single carrier, single-user data must be transmitted on consecutive RBs, which is easy to cause the number of RBs is not enough to transmit a user's data and wasted; user pairing is 1 to 1, such as the two users do not need the same size of the resource, which results in waste.

5G: Use single-carrier multi-carrier adaptive. Edge users use single-carrier, good coverage; mid- and near-point users use multi-carrier, users can be paired 1-to-many, user pairing is efficient, high resource utilization; user resource allocation can be used with discontinuous RB resources, there is a frequency selection gain, as well as the ability to fully utilize fragmented RB resources.

Sixth, channel coding

4G: service channel Turbo, control channel convolutional code, block coding, as well as repeated coding.

5G: LDPC code-service channel, high transmission rate for large data blocks, good demodulation performance, and low power consumption; Polar code-control channel, transmission of small data blocks, good demodulation performance, and coverage improvement of 1dB.

Seven, BF Weight Generation

4G: TM7/8 terminals: based on the terminal transmits the SRS, and the base station calculates the weight based on the SRS; TM9 terminal (R10 version and above): the terminal transmits SRS base station calculates the weights (middle and near points) and the terminal calculates PMI (far points) based on CRS adaptively.

5G: Terminal transmitting SRS base station calculates the weight (in the near point) with the terminal according to CRS calculates PMI (far point) adaptive; SRS needs full bandwidth to transmit, at the edge of the time due to the collection of power is limited, when it reaches the base station may have already been unable to recognize, and PMI system an index, only 1 ~ 2 RB can be sent to the base station, good coverage.

Eight, upstream and downstream conversion

4G: each frame (5ms/10ms) upstream and downstream conversion once, the delay is large.

5G: Larger carrier bandwidth and self-contained time slots for fast feedback and low latency.

Nine, large bandwidth

4G: maximum support for 20MHZ;

5G: maximum support for 100MHZ (C-band), 400MHZ (millimeter-wave);

Ten, carrier aggregation

4G: 8CC;

5G: 16CC;

Eleven, compared with the 4G capacity of the 5G Enhancement

1. Downlink

1); MM: flat

5G's most critical technology, dramatically improving spectral efficiency; LTE also has MM, and from LTE experience, MM's spectral efficiency is roughly about 5 times that of 2T2R

2); F-OFDM: 9% improvement

5G's bandwidth utilization has increased by 9% ;

3); 1024QAM: <5%

Peak improvement of 25%; however, considering the difficulty of accessing 1024QAM in the existing network, the predicted average throughput gain is less than 5%;

4); LDPC: unclear

5); more precise feedback: 20%~30%

Terminal SRS at the Terminal four antenna round send, the base station to obtain the terminal of all four channels of information, and make single-user multi-stream as well as multi-user between the MIMO scheduling and coordination is better; SRS and PMI adaptive, in the edge of the SRS is not allowed, the use of PMI is the BF effect is better compared to LTE.

6); overhead: basically flat

5G in the reduction of CRS at the same time, in fact, is an increase in CRI-RS and DMRS, less and increased overhead consistent, can not say that the CRS free, compared to LTE overhead is reduced. CRS free in fact, in order to reduce the interference of light load.

7) ; Slot aggregation: 10%

4G: DCI Grant information is sent for every two slots.

5G: Multiple slots are aggregated and only one DCI Grant message is sent, with low overhead.

2. Uplink

1); MM: flat

2); Single and Multi-Carrier Adaptive: 30%

User one-to-many unaligned pairing, RBs are not consecutively assigned;

3); LDPC: unknown

Twelve, 5G Compared to 4G Coverage Enhancements

1. ? Downlink

1) LDPC: Unknown

2) Power: 2dB