In the prior art, an important application of machine-type communication (MTC) user equipment (UE) is a smart meter. A smart meter is usually installed in a basement of a house, or is isolated by a metal casing. The MTC UE is subject to severer a path or penetration loss. Therefore, an operator expects a coverage area of a cell to be further enhanced, so that a service can be provided to MTC UE in an extreme environment (for example, located in a basement or located at an edge of a cell).
During enhancement of a coverage area, signal quality is usually improved by consuming more resources (for example, time resources, and/or frequency resources, and/or power resources, and/or code resources), and/or interference intensity is reduced through interference coordination.
In a wireless communications system, a random access process is usually required to establish a connection between user equipment and a network. An Long Term Evolution (LTE) network is used as an example, and a random access process of LTE has two modes: a contention-based mode and a non-contention-based mode. Contention-based random access includes four steps: Step 1 UE randomly selects one preamble from available preambles (preamble), and sends the randomly selected preamble on one available physical random access channel (PRACH) resource. Step 2 A base station replies to the detected preamble, where the reply message is included in a media access control packet data unit (MAC PDU). The MAC PDU includes one MAC header (header) and one or more random access response (RARs) and a possible padding (padding) bit.
The MAC PDU that carries the RAR may be referred to as a message 2 in short. The message 2 is carried by one physical donwlink shared channel (PDSCH). A physical donwlink control channel (PDCCH) or an enhanced physical donwlink control channel (EPDCCH) schedules transmission of the PDSCH. Therefore, the UE first needs to detect the PDCCH or the EPDCCH, to obtain scheduling information of the PDSCH, and further detect the PDSCH according to the scheduling information. If the UE successfully detects the PDSCH, and a preamble identified by an RAPID included in the MAC PDU carried by the PDSCH is a preamble sent by the UE, the UE believes that the base station has detected a preamble sent by the UE, and believes that an RAR corresponding to a subheader including the RAPID is an RAR sent by the base station to the UE. Step 3 After determining that the RAR fed back by the base station is received, the UE sends an RAR reply on a PUSCH (Physical Uplink Shared Channel, physical uplink shared channel), where the RAR reply is referred to as a h message 3 in short. The message 3 mainly includes a ue-Identity (user identity) and an establishment cause (a cause of an establishment request). Step 4 The base station detects the message 3 sent by the UE, determines that random access of the UE succeeds, and sends a random access contention resolution message to the UE, where the random access contention resolution message is referred to as a message 4 in short. The message 4 is also carried by the PDSCH. The PDCCH or the EPDCCH schedules transmission of the PDSCH. Therefore, the UE first needs to detect the PDCCH or the EPDCCH, to obtain scheduling information of the PDSCH carrying the message 4, and further detect the PDSCH according to the scheduling information. If the UE successfully detects the PDSCH, and the ue-Identity included in the message 4 carried in the detected PDSCH is the same as or matches the ue-Identity, of the UE, included in the message 3, the UE believes that random access succeeds.
It can therefore be seen that in a contention-based random access process, the foregoing four steps involves transmission of sequence, data, and scheduling (or control) information on six channels. A preamble sequence is transmitted on a PRACH channel, the scheduling information of the message 2 is transmitted on the PDCCH or the EPDCCH, the message 2 is transmitted on the PDSCH, the message 3 is transmitted on the PUSCH, the scheduling information of the message 4 is transmitted on the PDCCH or the EPDCCH, and the message 4 is transmitted on the PDSCH. In the foregoing cases, a coverage enhancement requirement is considered. If it needs to be ensured that random access of UE is performed reliably, performance needs to be enhanced for transmission of the foregoing six channels, which means that more resources need to be consumed, and complexity of implementing a base station and UE is greatly increased. Therefore, a mechanism is needed to simplify a random access process, so that implementation of coverage enhancement does not need to consume more resources, thereby reducing complexity of implementing a base station and UE.