Shulou(Shulou.com)06/01 Report--

Is 4G + a ghost again? What does it have to do with LTE-A? Let's start with LTE and LTE-A.

The full name of LTE, long-term-evolution, sounds a bit hasty. It is also called 3.9G. Its uplink peak speed and maximum bandwidth are slightly lower than 4G standard. What really brings the network to 4G is LTE-Advanced, that is, LTE-A.

LTE-An is a synonym for the evolution of LTE, which meets the needs of IMT-Advanced technology recruitment of ITU-R. It is not only an important source for 3GPP to form European IMT-Advanced technology proposals, but also a backward compatible technology, which is fully compatible with LTE and is an evolution rather than a revolution. Its technical specifications far exceed the minimum requirements of 4G.

The technical parameters of LTE-An are: bandwidth: 100MHz; peak rate: downlink 1Gbps, uplink 500Mbps; peak spectral efficiency: downlink 30bps/Hz, uplink 15bps/Hz.

LTE-An adopts key technologies such as carrier aggregation (Carrier Aggregation), uplink / downlink multi-antenna enhancement (Enhanced UL/DL MIMO), multi-point cooperative transmission (Coordinated Multi-point Tx&Rx), relay (Relay) and heterogeneous network interference coordination enhancement (Enhanced Inter-cell Interference Coordination for Heterogeneous Network), which can greatly improve the peak data rate, peak spectral efficiency, cell average spectral efficiency and cell boundary user performance of the wireless communication system. At the same time, it can also improve the efficiency of the whole network.

Is 4G + LTE-A? What are the actions of the three major operators?

The answer is no. 4G + is not LTE-A, but it is related to LTE-A.

In fact, the concept of 4G+ is first of all a new business brand launched by Telecom at the Tianyi Terminal Trading Expo on July 3, 2015. it is not a standard of 4G network technology, but a service or brand launched by operators.

After Telecom put forward the brand "Tianyi 4G +", Mobile followed suit. 4G + service was also released at the China International Information and Communications Exhibition on September 22, 2015, through three major measures: doubling network speed, doubling clarity and doubling affordability. to achieve a new upgrade of 4G.

At the same time, VoLTE is also a new service being promoted by China Mobile, which is characterized by no delay in dialing, high-fidelity calls and almost 100% restoration of sound quality. China Mobile said that it wants to achieve VoLTE across the network by mid-2016. In 2016, more than 100 VoLTE phones will be supported and sales will exceed 100 million. It is expected that 4G terminals will sell 330 million units for the whole year. There is no doubt that China Mobile has established a lead in 4G.

China Unicom has always had the most mature WCDMA network in the world, but its users were constantly eroded by insisting on the strategy of deep 3G and 4G integration at the initial stage of 4G. In the face of the loss of users for many quarters in a row, China Unicom could not sit still. In the afternoon of the communications exhibition, China Unicom issued a white paper on the new generation network architecture, making it clear that it will comprehensively accelerate 4G network construction in the future, and accelerate the deployment of 4G networks throughout the network, raising the network peak speed to 300m.

According to China Unicom, the population coverage of China Unicom's 4G network exceeded 90% in 2016. Three-carrier aggregation is realized commercially, and the peak rate of the network is increased to 330Mbps. In the future, we will actively promote the large-scale deployment of three-carrier, four-carrier, multi-carrier, 4G and WiFi convergence.

In terms of fixed-line broadband construction, China Unicom focuses on speeding up the transformation of optical fiber and accelerating the construction of "all-optical network".

At present, China Unicom has established its first "all-optical network province" in Shandong, and 39 cities across the country have built "all-optical network cities". China Unicom predicts that by 2016, all 10 northern provinces of China Unicom will achieve "all-optical network provinces".

In December 2015, Unicom held a "Wo 4G +" conference in Beijing and officially launched the "Wo 4G +" strategy, focusing on 4G network coverage, doubling network speed and calling experience.

What is the beauty of this 4G +, which the three operators are scrambling to withdraw from?

Unravel the mystery of 4G +, you will find that the reason why 4G + can achieve a faster rate than 4G is actually the use of LTE-A 's key technology carrier aggregation CA (Carrier Aggregation). Compared with the single carrier transmission of 4G, the 4G + we have seen so far is the result of the aggregation of dual carriers. Their peak rates are also slightly higher than those of 300Mbps.

So what is carrier aggregation?

Carrier aggregation is the aggregation of two or more carrier units (Component Carrier, CC) together to support larger transmission bandwidth. The maximum bandwidth per CC is 20 MHz. To make efficient use of fragmented spectrum, CA supports aggregation between different CC:

1) continuous CCs in the same frequency band

2) non-adjacent CCs in the same frequency band

3) CCs in different frequency bands.

Different types of carrier aggregation

Carrier aggregation is like a "glue", gluing scattered spectrum together and mixing transmission to provide faster rates.

Take the transport of goods as an analogy: a batch of goods (data from a UE), which could only be transported on one road (Cell or CC), can now be transported on multiple roads at the same time through CA. In this way, the amount of goods that can be transported at some point (throughput) has been significantly increased. The road conditions of each avenue may be different (frequency, bandwidth, etc.). There are more traffic points for those with good road conditions and less for those with poor road conditions.

With carrier aggregation technology, several other concepts have emerged: PCell and SCell.

PCell,SCell and Serving Cell:

Each CC corresponds to a separate Cell.

Primary Cell (PCell): the main cell is a cell that works in the main frequency band. UE performs the initial connection establishment process (connection establishment) in the cell, or starts the connection re-establishment process. During the handover process, the cell is indicated to be responsible for the RRC communication with the UE (see Section 3. 1 of 36.331).

Secondary Cell (SCell): an auxiliary cell, which is a cell that works in the secondary frequency band. SCell is added / modified / released through the RRC connection reconfiguration message RRCConnectionReconfiguration after the initial secure activation process (initial security activation procedure). Once the RRC connection is established, the sub-cell may be configured to provide additional wireless resources (see Section 3.1 of 36.331).

When UE is configured with CA, it uses the same C-RNTI in all Serving Cell.

Serving Cell: service cell, UE in RRC_ connected state, if CA is not configured, there is only one Serving Cell, that is, if PCell; is configured with CA, then the Serving Cell collection is composed of PCell and SCell (see Section 3.1 of 36.331) Serving Cell can refer to PCell or SCell.

A PCell is always active in RRC_CONNECTED mode, while one or more SCell may be active. Other SCells can only be configured in CONNECTED mode after the connection is established to provide additional wireless resources.

Simply take the above transportation as an analogy, PCell is equivalent to the trunk road, there is only one trunk road, which is not only responsible for transporting goods, but also responsible for communicating with the receiving end, telling the receiving end according to the receiving end's capacity (UE Capability) and how much goods are to be sent (load), which trunk roads to receive goods, as well as the basic situation of these trunk roads (PCell is responsible for RRC connection).

SCell is the equivalent of a secondary trunk road and is only responsible for transporting goods.

The receiving end (UE) needs to tell the shipper its ability, such as whether it can receive goods from multiple trunk roads at the same time, how many goods can be received on each trunk road at a time (UE Capability).

The shipper (eNodeB) can schedule the shipment according to the capacity of the peer (UE), otherwise it will be in vain for the receiver to handle it. (this is just the following behavior example, and UE may also be the shipper.)

Because different trunk roads may also carry another shipment (other UE data), different goods need to be distinguished, so the same batch of goods (belonging to the same UE) transmitted on different trunk roads have the same mark (C-RNTI).

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.