In 5G, frequency spectrum used is huge and country specific. In addition 5G will also use various types of Access networks like 2G, 3G, 4G, Wi-Fi and WiMAX to create a one Serving Area. At present, there is no single Mobile Handset that supports all these spectrum ranges due to practical difficulties / limitations of the current hardware available, its size and cost.
However, with the development in making advanced DSPs (small size, multi-core architecture, high clock speed and Million Instructions per Seconds [MIPS] capacity) and microprocessors, the hardware problem has been mitigated to a considerable extent. It is now possible for a device to support multiple frequency spectrums across a wide bandwidth. Having said that it is still a major challenge for the device’s to figure out which spectrum to choose.
This challenge can be addressed with the help of Software Defined Radio (SDR) in conjunction with Cognitive Radio (CR). With SDR and CR enabled hardware; users will able to roam across various geographies without worrying about the Frequency Spectrum used, there by getting more coverage / service area and network Operators will also able to generate more business by supporting range of devices (legacy and new, local and roaming subscribers).
CR is a radio that is aware of the environment and adapts functionality based on the environment. An SDR implies radio operations that can be controlled by software. An SDR enhances the functionality of CR through intelligent mechanism in software that would automatically re-configure the radio parameters, monitor the self performance, configure the environment around it (users, interference), senses the spectrum and interacts with the network using it. This is exactly what is required for Device to Device (D2D) and Mobile Type Communications (MTC). The intelligent Software of CR would work with the mobility management of device to select and hand off to identified network. This decision would be application aware so as to support D2D communication.
Application of SDR and CR in the device hardware for 5G will provide following advantages to both Operators and Subscribers,
- Reduced hardware and software that caters to multiple frequency spectrums in various geographies results in reduced cost and increased customer satisfaction
- Works like a normal radio with better performance and less cost as compared to the analogue counter parts
- Roaming and service continuity of 5G and Machine to Machine (falls under MTC) devices across geographies would be easy (no frequency spectrum restriction)
- Operator can provide services across different frequency spectrum covering wider Service Area and Subscriber would feel service coverage is more resulting better QoE.
- Less or no user intervention when Access Network (horizontal Handoffs) changes
- Very useful in public safety & emergency services, D2D and MTC communication as it is aware about its environment and power requirements.
One of the major problems of a CR with SDR for 5G systems is the tremendous power requirement to support the cognitive capability of the devices. Manufacturers are currently working on the hardware (chip sets) that will consume less power, battery technologies that will retain the charge for longer duration (for e.g. – lithium 4000 mAh batteries from Lenovo).
CR needs lot of intelligent mechanisms; most of which would be accomplished with SDR. However there are certain limitations in SDR to achieve it. For instance CR realization for 5G needs devices that scan and sense the entire range of spectrum with good sensitivity and quality. Further it would need multiple SDRs, its associated hardware and integration with the CR.
The CR and SDR adaptation has increased tremendously in Military and space instruments and applications. Cellular chipset manufacturers are not behind and also developing a common hardware that will cater to multiple access networks (Heterogeneous Networks) which would support varying frequency spectrum. Vendors like Marvell are producing System on Chip (SoC - PXA1936) that contains Dual SIM Dual Standby (DSDS) software for 5-mode modem that addresses the TD-LTE, FDD-LTE, TD-SCDMA, WCDMA and GSM wireless communication.
It looks like the time for SDR has come; CR would be the need for controlling SDR and interacting with the device’s platform. Use cases of D2D and M2M communications make CR/SDR a compelling need. To make this happen on all kinds of devices, a standardization based approach would be required. On the standardization front, cellular hardware / chip set vendors for devices are making SoCs but needs to have conformance with the SDR and CR standards. Also there is a need that both SDR forum and 3GPP standardization bodies need to work closely for Mobility management, Service continuity, QoS, D2D and MTC communication scenarios.