GPRS (General Packet Radio Service)
GPRS (General Packet Radio Service) is a method of enhancing 2G phones to enable them to send and receive data more rapidly. With a GPRS connection, the phone is "always on" and can transfer data immediately, and at higher speeds: typically 32 - 48 kbps. An additional benefit is that data can be transferred at the same time as making a voice call. GPRS is now available on most new phones.
GPRS is part of a series of technologies that are designed to move 2G networks closer to the performance of 3G networks. The key characteristic of a 3G network is its ability to transfer large amounts of data at high speed (up to 2 Mbps), enabling applications like video calling, video downloads, web browsing, email, etc. By increasing the speed of a 2G network, some of these applications become possible, e.g. web browsing and sending or receiving emails with large attachments. These technologies are called 2.5G and include enhancements to the CSD technology, such as HSCSD and EDGE.
GPRS Class Types:
The class of a GPRS phone determines the speed at which data can be transferred. Technically the class refers to the number of timeslots available for upload (sending data from the phone) or download (receiving data from the network). The timeslots used for data are in addition to the slot that is reserved for voice calls. These timeslots are available simultaneously, so the greater the number of slots, the faster the data transfer speed. Because GPRS transmits data in packets, the timeslots are not in use all the time, but are shared amongst all users of the network. That increases the overall data capacity of the network, and it also means that you are billed for the quantity of data transmitted, not the time that you are online. It may mean that during busy times, data transfer rates slow down, because the network will give priority to voice calls.
EDGE( Enhanced Data Rates for GSM Evolution)
Enhanced Data rates for GSM Evolution (EDGE) (also known as Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC)) is a backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM. EDGE is considered a 3G radio technology and is part of ITU's 3G definition.EDGE was deployed on GSM networks beginning in 2003— initially by Cingular (now AT&T) in the United States.
EDGE is standardized by 3GPP as part of the GSM family, and it is an upgrade that provides more than three-fold increase in both the capacity and performance of GSM/GPRS networks. It does this by introducing sophisticated methods of coding and transmitting data, delivering higher bit-rates per radio channel.
EDGE can be used for any packet switched application, such as an Internet connection. EDGE-delivered data services create a broadband internet-like experience for the mobile phone user. High-speed data applications such as video services and other multimedia benefit from EGPRS' increased data capacity.
Evolved EDGE continues in Release 7 of the 3GPP standard providing reduced latency and more than doubled performance e.g. to complement High-Speed Packet Access (HSPA). Peak bit-rates of up to 1Mbit/s and typical bit-rates of 400kbit/s can be expected.
Technology:
EDGE/EGPRS is implemented as a bolt-on enhancement for 2G and 2.5G GSM and GPRS networks, making it easier for existing GSM carriers to upgrade to it. EDGE/EGPRS is a superset to GPRS and can function on any network with GPRS deployed on it, provided the carrier implements the necessary upgrade.
EDGE requires no hardware or software changes to be made in GSM core networks. EDGE compatible transceiver units must be installed and the base station subsystem needs to be upgraded to support EDGE. If the operator already has this in place, which is often the case today, the network can be upgraded to EDGE by activating an optional software feature. Today EDGE is supported by all major chip vendors for both GSM and WCDMA/HSPA.
Transmission techniques :
In addition to Gaussian minimum-shift keying (GMSK), EDGE uses higher-order PSK/8 phase shift keying (8PSK) for the upper five of its nine modulation and coding schemes. EDGE produces a 3-bit word for every change in carrier phase. This effectively triples the gross data rate offered by GSM. EDGE, like GPRS, uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission. It introduces a new technology not found in GPRS, Incremental Redundancy, which, instead of retransmitting disturbed packets, sends more redundancy information to be combined in the receiver. This increases the probability of correct decoding.
EDGE can carry data speeds up to 236.8 kbit/s (with end-to-end latency of less than 150 ms) for 4 timeslots (theoretical maximum is 473.6 kbit/s for 8 timeslots) in packet mode. This means it can handle four times as much traffic as standard GPRS. EDGE meets the International Telecommunications Union's requirement for a 3G network, and has been accepted by the ITU as part of the IMT-2000 family of 3G standards. It also enhances the circuit data mode called HSCSD, increasing the data rate of this service. EDGE is part of ITU's 3G definition and is considered a 3G radio technology.
EDGE Evolution:
EDGE Evolution improves on EDGE in a number of ways. Latencies are reduced by lowering the Transmission Time Interval by half (from 20 ms to 10 ms). Bit rates are increased up to 1 MBit/s peak speed and latencies down to 800 ms using dual carriers, higher symbol rate and higher-order modulation (32QAM and 16QAM instead of 8-PSK), and turbo codes to improve error correction. And finally signal quality is improved using dual antennas improving average bit-rates and spectrum efficiency. EDGE Evolution can be gradually introduced as software upgrades, taking advantage of the installed base. With EDGE Evolution, end-users will be able to experience mobile internet connections corresponding to a 500 kbit/s ADSL service.
MIMO and OFDM
MIMO is applicable to all kinds of wireless communication technologies. However, the combination of MIMO and OFDM (Orthogonal Frequency Division Multiplex) has the following advantages. OFDM is adapted for multi-path propagation in wireless systems. The length of the OFDM-frames is determined by the Guard Interval (GI). This Gurad Interval restricts the maximum path delay and therefore the expansion of the network area. MIMO also uses the multi-path propagation.
OFDM is a wideband system with many narrowband sub-carriers. The mathematical MIMO channel model is based on a narrow band non-frequency selective channel. The latter is supported by OFDM as well. Fading effects in wideband systems normally occur only at particular frequencies and interfere with few sub-carriers. The data is spread over all carriers, so that only a small amount of bits get lost, and these can be
repaired by a forward error correction (FEC). OFDM provides a robust multi-path system suitable for MIMO. At the same time OFDM provides high spectral efficiency and a degree of freedom in spreading the time dimension of Space-Time Block Codes over several sub-carriers. This results in a stronger system based on the principle described previously
MIMO Standards:
Table 1 gives an overview of all current MIMO standards and their technologies. It is clear to see, that with the exception of 3GPP Release 7, all standards work with OFDM. The advantages of OFDM can obviously be linked to MIMO.
Table 1 MIMO Standards and the corresponding technology :
Standard Technology
WLAN 802.11n OFDM
WiMAX 802.16-2004 OFDM/OFDMA
WiMAX 802.16e OFDMA
3GPP Release 7 WCDMA
3GPP Release 8 (LTE) OFDMA
802.20 OFDM
802.22 OFDM
Handoff mechanism in Mobile WiMAX
For implementing a mobile network, a handoff mechanism must be defined to maintain uninterrupted user communication session during his/her movement from one location to another. Handoff mechanism handles subscriber station (SS) switching from one Base Station (BS) to another. Different handoff techniques have been developed. In general, they can be divided into soft handoff and hard handoff.
Figure. Soft Handoff
A SS maintains multiple connections. Delay is very minimal
Soft handoff is used in voice-centric cellular networks such as GSM or CDMA. It uses a make-before-break approach whereas a connection to the next BS is established before a SS leaves an ongoing connection to a BS. This technique is suitable to handle voice and other latency-sensitive services such as Internet multiplayer game and video conference. When used for delivering data traffic (such as web browsing and e-mail), soft handoff will result in lower spectral efficiency because this type of traffic is bursty and does not require continues handover from one BS to another.
Hard handoff in Mobile WiMAX
Figure. Hard Handoff
A SS maintains a connection to a single BS at any given time.
Mobile WiMAX has been designed from the outset as a broadband technology capable of delivering triple play services (voice, data, video). However, a typical Mobile WiMAX network is supposedly dominated by delay-tolerant data traffic. Voice in Mobile WiMAX is packetized (what is called VoIP) and treated as other types of IP packets except it is prioritized. Hard handoff (HHO) is therefore used in Mobile WiMAX. In hard handoff, a connection with a BS is ended first before a SS switches to another BS. This is known as a break-before-make approach. Hard handoff is more bandwidth-efficient than soft handoff, but it causes longer delay. A network-optimized hard handoff mechanism was developed for Mobile WiMAX to keep a handoff delay under 50 ms.
The 3G Long-Term Evolution RADIO INTERFACE CONCEPTS
The ability to provide high bit rates is a key measure for LTE. Multiple parallel data stream transmission to a single terminal, using multiple-input-multiple-output (MIMO) techniques, is one important component to reach this. Larger transmission bandwidth and at the same time flexible spectrum allocation are other pieces to consider when deciding what radioaccess technique to use. The choice of adaptive multi-layer OFDM, AML-OFDM, in downlink will not only facilitate to operate at different bandwidths in general but also large bandwidths for high data rates in particular. Varying spectrum allocations, ranging from 1.25 MHz to 20 MHz, are supported by allocating corresponding numbers of AML-OFDM subcarriers. Operation in both paired and unpaired spectrum is possible as both time-division and frequency-division duplex are supported by AML-OFDM.
A. Downlink – OFDM with Frequency-Domain Adaptation
The AML-OFDM-based downlink has a frequency structure based on a large number of individual sub-carriers with a spacing of 15 kHz. This frequency granularity facilitates to implement dual-mode UTRA/E-UTRA terminals. The ability to reach high bit rates is highly dependent on short delays in the system and a prerequisite for this is short sub-frame duration. Consequently, the LTE sub-frame duration is set as short as 0.5 ms in order to minimize the radio-interface latency. In order to handle different delay spreads and corresponding cell sizes with a modest overhead the OFDM cyclic prefix length can assume two different values. The shorter 4.7 ms cyclic prefix is enough to handle the delay spread for most unicast scenarios. With the longer cyclic prefix of 16.7 ms very large cells, up to and exceeding 120 km cell radius, with large amounts of time dispersion can be handled. In this case the length is extended by reducing the number of OFDM symbols in a sub-frame.
OFDM is suitable for broadcast services. To support such services the same information is transmitted from several (synchronized) base stations to the terminal. The total signal the terminal receives from the base stations will appear as multipath propagation and thus implicitly be exploited by the OFDM receiver. The longer cyclic prefix allows combining
broadcast signals from a large number of distant base stations. Techniques to exploit channel variations in the time domain have been successfully implemented for HSDPA. This has resulted in a substantial increase in spectral efficiency. For EUTRA, the channel-based adaptation can be extended to also include transmission adaptation in the frequency domain thanks to the use of OFDM. When the radio channel varies significantly over the system bandwidth, large performance gains can be achieved.
B. Uplink – Single-Carrier FDMA with Dynamic Bandwidth
A key requirement for uplink transmission is that the transmission should allow for power-efficient user-terminal transmission to maximize coverage. To reach this, single-carrier frequency-division multiple access (FDMA) with dynamic bandwidth is a good choice. In order to achieve intra-cell orthogonality, the base station assigns a unique time-frequency interval to the terminal for the transmission of user data. This is done for each time interval. The users are separated primarily by time-domain scheduling; however, if the terminal has a limited transmission power or not enough data to transmit, also frequency-domain scheduling is used.
C. Multi-Antenna Solutions
Advanced multi-antenna techniques will play an important role in fulfilling the 3G LTE requirements on increased data rates and improved coverage and capacity. This includes both beamforming and multi-layer transmission solutions to better exploit the potential of using the spatial domain. This potential is large and not always fully exploited in existing radio access technologies. Increasing data rates can be achieved by transmitting multiple parallel streams or layers to a single user. This Multi-layer transmission is often referred to as MIMO. The preferred use for MIMO is in conditions with favorable signal-to-noise ratio and rich scattering in the radio channel, e.g., small cells or indoor deployments. Multi-layer transmission may be applied for downlink as well as uplink transmission. The receiver has the possibility to separate the multiple data streams by using the channel properties and knowledge of the coding scheme. In order for the receivers to solve this task it is necessary to standardize the multi-layer transmission scheme selected for the long-term 3G. Selective per-antenna rate control (S-PARC) is an interesting technique where the number of layers and the data rate per layer, is adapted to the instantaneous channel conditions.
Beamforming implies that multiple antennas are used to form the transmission or reception beam and, in this way, increase the signal-to-noise ratio at the receiver. This technique can both be used to improve coverage of a particular data rate and to increase the system spectral efficiency. The increased signal-to-noise ratio is not only due to a larger gain in the direction of the desired user, but also due to a better control of the spatial interference distribution in the cell. Beamforming can be applied both to the downlink and the uplink. It is possible to make beamforming transparent to the terminal, which would eliminate the need to standardize a particular solution. Instead, the exact algorithms can evolve over time and be tailored to particular needs. Alternatively, one could include some explicit support for a specific beamforming solution, especially if that would increase the efficiency of the system and enable low complexity implementations.
It is also possible to combine multi-layer transmission and beamforming. An example of this would be to transmit two data streams with two groups of antennas, where beamforming is employed within each group. Beamforming is then used to increase the received signal-to-noise ratio and multi-layer transmission is applied to convert the increased signal-to-noise ratio into a higher data rate.
HSPDA - the next step for 3G
With 3G networks spreading throughout the globe, consumers are just now beginning to experience the true capabilities of 3G wireless services. Already, some fear that demands for high-speed data access will exceed the capability of today's UMTS networks. Fortunately, the wireless industry already has plans in place for enhanced data networks.
Among the next-generation contenders in the ring are Flarion's Flash OFDM (F-OFDM), WiMAX (IEEE802.16e) and CDMA2000 1XEV-DO. But it's high-speed downlink packet access, or HSDPA, that enables a smooth, cost-efficient upgrade to existing W-CDMA networks at minimal cost.
HSDPA's incremental UMTS network upgrade aims to increase user peak data rates and quality-of-service and improve spectral efficiency - much like EDGE and 1XRTT have done for 2G. Although UMTS enables streaming video, broadband Internet access and video conferencing, HSDPA offers peak downlink data rates of up to 14 Mbps - dramatically more than the 384 kbps that is typical of today's UMTS and the highest data rate of any available mobile WAN technology.
HSPDA works by moving important processing functions closer to the air interface. Although current UMTS networks perform network scheduling and retransmission in the radio network controller, HSDPA moves these functions to the base station (called Node B in UMTS systems), allowing scheduling priority to take account of channel quality and terminal capabilities. Retransmission also benefits from hybrid automatic retransmission request in which retransmissions are combined with prior signal transmissions to improve overall reception. HSDPA adds a channel-sharing mechanism that allows several users to share the high-speed air interface channel and other technological advances such as adaptive modulation and coding, quadrature amplitude modulation and channel quality feedback. These enhancements allow HSDPA to roughly double the total throughput capacity of a network.
For consumers, that translates into shorter service response times, fewer waits and faster connections. Wireless users can talk on the phone while simultaneously downloading packet data. Most important, they can use their wireless handsets to download Web pages, audio or video at speeds well above the performance they are accustomed to with landline-based DSL or even cable Internet connections.
What's good for the consumer ultimately is good for the operator, provided the costs and barriers to deployment are not too great. HSDPA significantly enhances W-CDMA with little hardware investment. It operates in 5 MHz channels and is backward-compatible with current W-CDMA networks. This allows network operators to introduce greater capacity and higher data speeds on the same carriers as with existing Release '99 W-CDMA services. A system may be upgraded incrementally to enhance performance for users of the latest handsets without losing network capacity or interrupting service to subscribers who rely on older handset technology.
As an extension of GSM, HSDPA can be deployed readily in the United States, Europe and Japan. In fact, some service providers may introduce pilot projects within the next year. By 2007, HSDPA likely will be a leading technology worldwide. This means that operators will be able to offer global roaming capabilities based on infrastructure already in place today and serving a sizable handset base, including older W-CDMA units.
HSDPA's incremental upgrade and dramatic performance benefits will serve as the best stepping stone to 4G for many operators. Texas Instruments is working within the 3G Partnership Project (3GPP) to enhance the standard in ways that will provide continuing business opportunities for wireless operators.
Among the developments we see down the road is high-speed uplink packet access (HSUPA), which will augment HSDPA to create a more symmetrical high performance system. We also expect ongoing improvements to boost network efficiency, reduce latency and increase overall network throughput.
All of this can be achieved through incremental upgrades to time proven W-CDMA technology. The HSDPA standard has been in place for a couple of years. Base station equipment is now starting to reach the market and handsets will follow, with widespread deployment anticipated in 2006 and 2007.
For consumers, HSDPA will help 3G technology fulfill its promise with more sophisticated data applications and better performance. For operators, this technology enables a highly competitive network with only incremental enhancements to existing infrastructure. HSDPA promises to provide a better return on investment and stronger revenues per megabit delivered compared to other avenues to very high-speed service.
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