Cellular systems in general suffer from co-channel interference. For example, simultaneous transmissions may use the same physical resources and thus generate mutual interference. This co-channel interference reduces the signal quality, which may be measured as signal to interference plus noise ratio (SINR). The reduced signal quality in turn reduces the system capacity.
Future wireless networks, e.g. 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) and 3GPP LTE Advanced, with a more dense deployment of access nodes, e.g. base stations (BSs), or with a higher density of users will most probably remain interference-limited.
There exist proposals to use an approach of cooperative signal communication, e.g. in 3GPP LTE Advanced which refers thereto as cooperative multipoint transmission and reception (COMP). In this approach, receive (Rx) signals are collected from a plurality of BSs for implementing uplink (UL) cooperation, and transmit (Tx) signals are transmitted from a plurality of BSs for implementing downlink (DL) cooperation.
In UL cooperation, several receiving access nodes, e.g., base stations (BSs) or remote radio heads (RRHs), receive a signal from a mobile terminal, also referred to as user equipment (UE), thereby obtaining multiple Rx signals from the terminal. The Rx signals are then communicated between access nodes and jointly processed, e.g. at a central node or at a serving BS.
In DL cooperation, a central node or a serving BS distributes a Tx signal to several transmitting access nodes, e.g. BSs or RRHs. The transmitting access nodes jointly transmit the signal to the terminal.
In both cooperation scenarios, signals may be processed, i.e. by joint reception in UL or joint pre-coding in DL, at a central node or at a serving access node so that co-channel interference is mitigated. Furthermore, the cooperative signal reception or transmission may increase the carrier signal strength.
In the approach of cooperative signal communication, cooperating communication nodes, i.e. receiving access nodes and/or transmitting access nodes, need to quantize analogue information in order to communicate it in a digital way to other access nodes. Parameters of the quantization process, e.g. the quantization depth which may be defined as the amount of bits per analogue value, determine the amount of communicated information and the required transport capacity. For example, the higher the quantization depth, the larger is the amount of communicated information. The smaller the quantization depth, the smaller is the required transport capacity.
A typical design criterion when implementing a quantization process is the distance between the expected/perceived value and the quantized value. For example, quantizers for signal detection can be configured to perform optimally under a given Signal-to-Noise ratio (SNR). If the SNR varies over time, one known approach is to design a fixed quantizer for an approximated SNR. The fixed quantizer is then used irrespective of the actual SNR.
When using cooperative signal communication, e.g. in COMP-enabled systems, the exchange of Rx or Tx signals, especially In-Phase/Quadrature (IQ) samples, causes a lot of traffic between BSs or other nodes. The resulting data traffic capacity requirement depends, among others, on the number of cooperating access nodes. Accordingly, situations may occur in which it is not possible to use cooperative signal communication with a desired number of cooperating access nodes due to insufficient data traffic capacity between the access nodes. On the other hand, providing a communication network with increased data traffic capacity for communication between access nodes or other nodes may require significant resources.
Accordingly, there is a need for techniques that overcome the aforementioned problems and allow for efficiently implementing a communication network enabled for cooperative signal communication.
USPTO Backgrounds
USPTO Backgrounds