NB-IoT and eMTC belong to the cellular Internet of Things, and also have the "3C" feature of the cellular Internet of Things:
Coverage enhanced coverage
Cost low cost
In order to meet the "3C" goal, the implementation of NB-IoT and eMTC is also different, as follows:
Comparison of key technologies between NB-IoT and eMTC
The coverage target of NB-IoT is MCL 164dB, and its coverage enhancement is mainly achieved by increasing the uplink power spectral density and repeated transmission.
The coverage target of eMTC is MCL 155.7dB, and its power spectral density is the same as that of LTE. Coverage enhancement is mainly achieved by repeated transmission and frequency hopping.
MCL, (Maximum Coupling Loss), refers to the path loss from the base station antenna port to the terminal antenna port. From the coverage target, eMTC is about 8dB lower than NB-IoT.
How to increase the coverage by repeating the transmission?
Repeated transmission is the transmission of one transport block in multiple subframes. Repetition Gain=10log Repetition Times, which means that 2 times retransmission can increase 3dB. NB-IoT can support up to 2048 retransmissions and 128 retransmissions.
Both NB-IoT and eMTC use repeated transmission to enhance coverage.
How to increase the uplink power spectral density to enhance coverage?
The uplink and downlink control information and the service information are transmitted in a narrower LTE bandwidth, and the PSD (Power Spectrum Density) gain under the same transmission power is larger, which reduces the demodulation requirement of the receiver.
In the downlink direction, if the NB-IoT adopts the independent deployment mode, the downlink transmit power can be independently configured, and its power spectral density is the same as that of GSM, but is about 14 dB higher than the LTE FDD power spectral density.
In the uplink direction, since the minimum scheduling bandwidth of NB-IoT is 3.75K or 15K, the uplink power spectral density is enhanced by 17dB at the maximum. Considering that the GSM terminal transmission power can be up to 33dBm and the NB-IoT transmission power is up to 23dBm, the actual NB-IoT terminal ratio is The power spectral density of the GSM terminal can be up to about 7 dB.
eMTC shares the transmission power and system bandwidth with LTE, and has no enhancement in power spectral density. The coverage enhancement is mainly achieved by repeated transmission and frequency hopping.
For NB-IoT, it is worth mentioning that:
In the downstream direction, only independently deployed power can be configured independently. The power of the in-band and guardband deployment modes is limited by the power of LTE. Therefore, in the in-band and guardband deployment modes, NB-IoT needs more retransmissions. The number of times is comparable to the level of coverage comparable to the standalone deployment model.
In the upstream direction, the three modes are basically the same.
Low power consumption
At low power consumption, NB-IoT and eMTC use the same technology, including: PSM, eDRX, and extended cycle timers.
The phone needs to be on standby, otherwise someone can call you can't find what to do? But this means that the phone needs to monitor the network from time to time, which is to consume power.
However, the IoT terminal is different from the mobile phone. Most of the time, it is in a deep sleep state. After reporting one or two messages every day or even every week, after staying in the idle state for a period of time, it enters the deep sleep state without listening to the air interface message.
PSM is to let the IoT terminal enter the deep sleep state after sending the data, similar to the shutdown, without any communication activities.
DRX (Discontinuous Reception), that is, discontinuous reception. eDRX is an extended discontinuous reception.
The mobile phone can receive signals intermittently to save power. NB-IoT and eMTC extend this intermittent interval to save power.
3 extended cycle timer
Flexible configuration of the long-cycle position update timer RAU/TAU to reduce the number of wake-ups.
How to reduce costs, including reducing protocol stack processing overhead, single antenna and FDD half-duplex mode to reduce RF cost, low speed and low bandwidth itself means reducing the complexity of chip processing and so on.
For example, the FDD half-duplex mode means that it is not necessary to handle both transmission and reception at the same time, which is cheaper and more power-efficient than full-duplex.
Comparison of technical parameters between NB-IoT and eMTC
NB-IoT pursues the lowest cost, the longest battery life, no mobility, and very low data rate. It is suitable for no mobility, small data volume, insensitive to delay, sensitive to cost, terminal order of magnitude. Large applications such as smart parking, smart light poles, smart meter reading, etc.
In order to meet more application scenarios and market demands, Re-14 and subsequent versions will implement a series of enhancement technologies for NB-IoT, including increased positioning and multicast capabilities, providing higher data rates on non-anchor carrier. Paging and random access are performed, the mobility of the connected state is enhanced, and the lower UE power level is supported.
eMTC supports voice, has a fast transmission rate and supports mobility, but the module cost is relatively high, and is suitable for wearable devices, health monitoring, indoor mobile applications, and the like.
Comparison of NB-IoT and eMTC deployment methods
NB-IoT deployment mode
NB-IoT is divided into three deployment methods: Stand alone, Guard band, and In-band.
Independent deployment is suitable for re-cultivating the GSM band. The channel bandwidth of GSM is 200KHz, which just creates space for the NB-IoT 180KHz bandwidth, and there is a 10KHz guard interval on both sides.
The guard band deploys resource blocks that utilize unused 180KHz bandwidth in the LTE edge guard band.
In-band deployment utilizes any resource block in the middle of the LTE carrier. However, in the in-band deployment mode, some PRBs, NB-IoT can not be used.
eMTC deployment mode
eMTC supports deployment with LTE and also supports independent deployment.
It mainly adopts LTE in-band deployment mode and supports TDD and FDD. eMTC and LTE work together in the same frequency band, and the base station uniformly allocates resources and shares part of the control channel. Therefore, operators can deploy eMTC directly in the existing LTE frequency band without having to allocate separate spectrum.
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