In future wireless communication networks or systems there will be a mixture of multiple types of access nodes or elements with large coverage cells (Macro cells) and small coverage cells (micro/pico/femto cells), with whole or partly overlapping coverage areas. For example, a communication network or system such as a Wide Area Network may use macrocells, picocells, and/or femtocells in order to offer wireless coverage in an environment with a wide variety of wireless coverage areas, ranging from an open outdoor environment to office buildings, homes, and underground areas. Such communication networks or systems may include handoff capability between the macro and small coverage areas. This type of communication network deployment is the so-called Heterogeneous Network deployment (HetNet), which has the capability of handling the large traffic growth predicted in future wireless communication networks and may also extend network coverage to areas with no macro coverage.
Other examples of communication networks or systems that may be used or combined to form a communication network or system such as a HetNet may include, but are not limited to, any communication network or system employing large or macro cells and small or low power cells for serving UEs, or one or more networks or systems having large and/or small cells such as packet or circuit switched network(s), IP based networks, legacy PS networks such as the second generation (2G) or 2.5 generation (2.5G) (e.g. Global System for Mobile Communications (GSM), cdma2000, Wideband Code Division Multiple Access (W-CDMA), third generation (3G) (e.g. Universal Mobile Telephone System (UMTS)), and fourth generation and beyond (4G and beyond) type networks (e.g. networks based on Long Term Evolution (LTE) and LTE-Advanced systems), and/or evolved packet switched (EPS) networks, and/or all internet protocol (IP) based PS networks, Internet Protocol Multimedia Subsystem (IMS) core networks, IMS service networks, microcell/picocell/femtocell networks, IEEE standard 802.11 or Wi-Fi networks for use in offloading traffic from radio access networks (RAN) or mobile networks and the like.
The UE may comprise or represent any device used for communications over a communication network. Examples of a UE that may be used in certain embodiments of the described communication networks are, but are not limited to, wireless devices such as mobile phones, mobile devices, terminals, smart phones, portable computing devices such as lap tops, handheld devices, tablets, netbooks, computers, personal digital assistants and other wireless communication devices. Typically, the output power from the access nodes of small cells (e.g. low power node) is several times smaller compared to the output power of the access nodes of macro cells (e.g. base stations). This difference can create an imbalance between the uplink and downlink of the access nodes of small cells. A communications network (e.g. HetNets) that has a large difference in output power amongst its cells will have different optimum cell borders for the uplink and downlink channels for each access node serving each cell. Conventional uplink power control may be used as described in Third Generation Partnership Project Technical Specification 36.213, section 5, in an attempt to combat the differences in output power amongst the UEs in each cell of the communication network. However, typically such uplink power control is only useful in a homogenous communication network, where each cell does not sufficiently interfere with other cells. In a communication networks having macro cells and small low power cells, (e.g. a HetNet) it is difficult to optimise the network performance in both macro cells and small low power cells using traditional uplink power control methods.
FIGS. 1 and 2 are schematic illustrations of an example communication network or system 100 that includes a small cell 102 with a low power access node 104 (e.g. a low power node) serving a user equipment (UE) 106. The communication network 100 also includes a macro cell 108 with an access node 110 (e.g. a base station) serving another UE 112.
FIG. 1 illustrates the macro cell 108 and small cell 102 defining a path loss (PL) border and a Reference Signal Received Power (RSRP) border. The RSRP border for the small cell 102 is located where a UE 106 in the small cell 102 experiences the same received power for downlink signals from the access node 110 of the macro cell 108 and downlink signals from the access node 104 of the small cell 102. The PL border for the small cell 102 is located where the UE experiences the same path loss for the downlink signals of the macro cell 108 and small cell 102. As can be seen, even though the PL boarder for the cell edge of the small cell 102 is larger, the RSRP border results in a smaller coverage area for the small cell 102. This cross over may determine the small cell 102 uptake area, i.e. the area when macro cell UEs 112 move into the coverage of the small cell 102, and vice-versa for small cell UEs 106.
As illustrated in FIG. 2, a macro user using UE 112 close to or on the cell edge of the small cell 102 may cause interference with UE 106 in the small cell 102. The UE 112 has a lower path loss to the small cell 102, which means the UE 112 of the macro user can cause a lot of interference to the small cell 102 and also to each UE 106 within the small cell 102. In this example, with only one macro cell UE 112, the signal-to-interference-plus-noise ratio experienced by UE 106 (SINRUE1) may be expressed as SINRUE1=P1G11/(P2G21N0), where P1 is the uplink transmit power of UE 106 of the small cell 102, G11 is the uplink path loss from UE 106 of the small cell 102 to the access node 104 of the small cell 102, P2 is the uplink transmit power of UE 112 of the macro cell 108, G21 is the uplink path loss from UE 112 of the macro cell 108 to the access node 104 of the small cell 102, and N0 is the noise such as additive white Gaussian noise experienced by UE 106. It is clear that a macro cell UE 112 on the edge of the macro cell 108 will experience a lower uplink path loss, G21, to the access node 104 of the small cell 102 compared with the uplink path loss, G22, to the access node 110 of the macro cell 108. This means that the macro cell UE 112 will cause a lot of interference to the small cell UE 106. One way to combat the increase in uplink interference is to increase the received/transmitted signal strength, e.g. received/transmitted signal strength target (P0) or the uplink power control target, on the uplink used by each UE 106 in the small cell 102 by a power offset (Poffset). Another possibility is to use SINR based closed loop uplink power control in the small cell 102. For simplicity and by way of example, P0 is used to represent the received signal strength target for the uplink signal associated with UE 106 received by node 104 of small cell 102. It is to be appreciated, that P0 could alternatively be an transmit signal strength target for the uplink signal associated with UE 106 transmitted by UE 106 to node 104 of small cell 102.
FIG. 3 is an illustration of four scenarios 301, 302, 303 and 304 showing how the performance for a UE 106 in the small cell 102 (e.g. a pico cell) changes with different uplink power control settings in relation to a received signal strength target (P0) at the access node 104 of the small cell 102. Each scenario represents a graph of the user throughput (e.g. User Thput) in Megabits per second (Mbps) vs time in seconds. In each graph, the throughput performance of the small cell UE 106 (e.g. pico cell user) is illustrated with a line and circles and the throughput performance of the macro cell UE 112 (e.g. macro cell user) is illustrated with a line and squares.
Initially, the small cell UE 104 transmits for 5 seconds, after which the macro cell UE 112 beings to transmit and both the small cell UE 104 and macro cell UE 112 transmit for a further 18 seconds.
In scenario 301, the received signal strength power target (P0) for the small cell UE 104 and the macro cell UE 112 that is received at the access node 104 of the small cell 102 are set at −103 dBm. Initially, the small cell UE 106 has excellent throughput performance of around 40 Mbps, however, once the macro cell UE 112 begins transmitting the throughput performance of the small cell UE 106 drops significantly to around 1 Mbps, while the macro cell UE 112 enjoys a throughput performance of around 35-38 Mbps.
In scenario 302, the received signal strength power target (P0) for the small cell UE 104 is set to −100 dBm and that of the macro cell UE 112 is set to −103. Initially, the small cell UE 106 has excellent throughput performance of around 40 Mbps, however, once the macro cell UE 112 begins transmitting the throughput performance of the small cell UE 106 still drops significantly to around 2-3 Mbps, while this is an improvement, it is evident that the macro cell UE 112 degrades further to around 31-33 Mbps.
In scenario 303, the received signal strength power target (P0) for the small cell UE 104 is set to −97 dBm and that of the macro cell UE 112 is set to −103. Initially, the small cell UE 106 has excellent throughput performance of around 40 Mbps, however, once the macro cell UE 112 begins transmitting the throughput performance of the small cell UE 106 still drops significantly to around 5 Mbps, while this is an improvement, it is evident that the macro cell UE 112 degrades further to around 30 Mbps.
In scenario 304, the received signal strength power target (P0) for the small cell UE 104 is set to −87 dBm and that of the macro cell UE 112 is set to −103. Initially, the small cell UE 106 has excellent throughput performance of around 40 Mbps, however, once the macro cell UE 112 begins transmitting the throughput performance of the small cell UE 106 still drops to around 15-17 Mbps, while this is an improvement, it is evident that the macro cell UE 112 significantly degrades further to around 11-12 Mbps.
As in scenario's 303 and 304, setting the high target of P0 to greater than −97 dBm maximizes the throughput performance of the small cell UE 106, but, at the same time, the macro UE 112 throughput performance can significantly degrade when the small cell received signal strength target (or uplink power control target) (P0) is increased. For macro UEs 112, the small cell 102 should use a low received signal strength target (e.g. a low P0 target).
As can be seen, simply increasing the received signal strength target (P0) for small cell UEs 106 in the small cell 102 can have a dramatic impact on the macro cell UEs 112 and vice versa. There is a need for a method to carefully tune the uplink power control so that small cell 102 performance is improved while at the same time minimising the impact or even maintaining performance and coverage for UEs 112 in the macro cell 108.