Because mobile devices are equipped with a limited amount of battery power, it is essential to have efficient power management mechanisms in mobile broadband networks such as mobile WiMAX and 3GPP Long Term Evolution that enable always on connectivity. This article presents the state-of-the-art power management methods in next-generation wireless networks with a focus on IEEE 802.16m based next-generation WiMAX networks and 3GPP LTE. To minimize and optimize user equipment power consumption, and further to support various services and large amounts of data transmissions, advanced power conservation mechanisms are being developed in IEEE 802.16m and 3GPP. Two advanced power conservation mechanisms, sleep and idle modes, which are enhanced versions of the legacy IEEE 802.16 system’s sleep and idle modes, were proposed and adopted in IEEE 802.16m. Similarly, 3GPP LTE adopts a discontinuous reception mechanism for power conservation in RRC_CONNECTED and RRC_IDLE states. Power management techniques in WiMAX and 3GPP LTE provide less control signaling and operational overhead while providing more efficient power saving, and use simpler operation procedures than the existing power management techniques.
INTRODUCTION
With the proliferation of wireless services and anytime anywhere communication providing always on connectivity, mobile devices are getting smaller and smarter. Therefore, next-generation wireless standards, such as IEEE 802.16m and Third Generation Partnership Program (3GPP) Long Term Evolution (LTE), should provide very efficient power conservation mechanisms to achieve longer battery life while providing enhanced user experience and quality of service (QoS).
Mobile stations (MSs) are not always engaged, in active communications. For significant durations, MSs are waiting for incoming or outgoing packets. These standby periods can be used for power conservation. The power management methods for existing voice-dominant wireless systems are designed based on the following principles. The circuit-switched voice traffic pattern is deterministic in nature (i.e., continuous traffic during a voice call followed by no traffic after the call is over). Therefore, keeping the radio on during the voice call and using idle mode while the mobile node is not on a call works best. As voice calls have low data rates, the devices use a small frequency band and/or time period for transmission/reception operations. Finally, the total average talk time per day by an average mobile phone user is not high. On the other hand, traffic in next-generation broadband wireless systems is bursty with significant periods of no traffic during a session (e.g., reading time during a web browsing session). Therefore, it is inefficient to keep the radio on during the entire session. Users spend significant amounts of time using different mobile Internet applications. Thus, the always on feature of mobile Internet consumes significant power. Finally, as the average data rate used by Internet applications is very high, the devices have to use a larger frequency band and/or time period for transmission/reception operations. Due to these reasons, the power management techniques of voice-oriented wireless networks are not applicable for next-generations wireless data networks. This paper provides a technical overview of power management in IEEE 802.16m and 3GPP LTE.
OVERVIEW OF WIMAX AND 3GPP LTE
WiMAX
WiMAX, also known as IEEE 802.16, provides wireless data services by using the 10-66 GHz frequency bands and provides data rates up to 70 Mbps over distance of 50 km. WiMAX covers large geographical areas using licensed or unlicensed spectrum in order to provide wireless Internet services to users with high data rates. It is based on WMAN which is not only an alternative to wired T1 and Digital Subscriber Lines (DSL) but it also provides wireless broadband services within a building from an Internet Service Provider (ISP) and can be used to connect many Wi-Fi networks across different campuses or cities.
WiMAX works like any other cellular technology and uses a base station to establish the wireless connection to the subscriber such as Universal Mobile Telecommunication Systems (UMTS). The communication between two or more WiMAX base stations could be Point to Point/ Line of Sight (LOS) whereas between the base station and the subscriber can be Point to Multi Point/ Non Line of Sight (NLOS).
IEEE 802.16 Standards
Telecommunication equipment manufacturers started introducing products for Broadband Wireless Access (BWA) at the end of the 90’s. But they were still looking for interoperable standard. The National Wireless Electronics Systems Testbed (N-WEST) called a meeting in 1998, about the need of an interoperable standard which resulted in the IEEE 802 standard. A lot of efforts were made in this regard which resulted later in the formation of IEEE 802.16 standard. Initially, the main focus of this group was to develop the radio interface for Broadband Wireless Access (BWA) which used the radio spectrum from the 10-66 GHz range. It also supports the LOS based Point to Multipoint (PMP) broadband wireless system.
3GPP Long Term Evolution
The 3rd Generation Partnership Project (3GPP) started working on 3G cellular system evolution in November, 2004. The 3GPP is the collaboration agreement for promotion of mobile standards in order to cope future needs (high data rates, spectral efficiencies, etc.). The 3GPP LTE (Long Term Evolution) was developed to provide higher data rates, lower latencies, wider spectrum and packet optimized radio technology.
Like other cellular technologies LTE uses OFDM as multiplexing technique. LTE uses OFDMA as downlink and Single Carrier FDMA (SC FDMA) as uplink transmission technique. The use of SC FDMA in LTE reduces the Peak to Average Power Ratio (PAPR) which is the main drawback of OFDM.
LTE uses wider spectrum, up to 20 MHz, to provide compatibility with existing cellular technologies such as UMTS and HSPA+, and increases the capacity of the system. LTE uses flexible spectrum which makes it possible to be deployed in any bandwidth combinations. This makes LTE suitable for various sizes of spectrum resources.
LTE uses both FDD and TDD as duplexing techniques to accommodate all types of spectrum resources.
Possibilities for Power Saving
In mobile networks an MS can be in one of the following states:
• State I: Receive or send traffic
• State II: Do not receive or send traffic while in active session(s)
• State III: Not in an active session
When an MS is in either state II or III, it can temporarily shut down its transmitter and receiver for power saving. During states II and III, sleep mode/discontinuous reception (DRX) in RRC_CONNECTED state and idle mode/DRX in RRC_IDLE state can be used in WiMAX/3GPPLTE.
The mapping of power management modes to a generic traffic model is shown in Fig. 1 where the MS sends/receives bursts of packets followed by inter-burst intervals. The time interval between consecutive sessions is the inter-session interval. Depending on the state of traffic, an MS remains in one of the following operational modes: connected mode, power management mode in state II (sleep mode —IEEE 802.16m, DRX in RRC_CONNECTED — 3GPP LTE), and power management mode in state III (idle mode — IEEE 802.16m, DRX in Time RRC_IDLE — 3GPP LTE).
The above conference Report is not complete, few image are there which i haven't upload.
0 comments:
Post a Comment
Thanks for your Valuable comment