09-05-2012, 05:11 PM
GLOBAL ROAMING
[attachment=21723]
. Introduction
The last few years have witnessed a phenomenal growth in the wireless industry, both in terms of mobile technology and its subscribers. There has been a clear shift from fixed to mobile cellular telephony, especially since the turn of the century.By the end of 2010, there were over four times more mobile cellular subscriptions than fixed telephone lines Both the mobile network operators and vendors have felt the importance of efficient networks with equally efficient design.This resulted in Network Planning and optimization related services coming in to sharp focus.With all the technological advances, and the simultaneous existence of the 2G, 2.5G and 3G networks, the impact of services on network efficiency have become even more critical. Many more designing scenarios have developed with not only 2G networks but also with the evolution of 2G to 2.5G or even to 3G networks. Along with this, inter-operability of the networks has to be considered.1G refers to analog cellular technologies; it became available in the 1980s. 2G denotes initial digital systems, introducing services such as short messaging and lower speed data. CDMA2000 1xRTT and GSM are the primary 2G technologies, although CDMA2000 1xRTT is sometimes called a 3G technology because it meets the 144 kbps mobile throughput requirement. EDGE, however, also meets this requirement. 2G technologies became available in the 1990s. 3G requirements were specified by the ITU as part of the International Mobile Telephone 2000 (IMT-2000) project, for which digital networks had to provide 144 kbps of throughput at mobile speeds, 384
kbps at pedestrian speeds, and 2 Mbps in indoor environments. UMTS-HSPA and CDMA2000 EV-DO are the primary 3G technologies, although recently WiMAX was also designated as an official 3G technology. 3G technologies began to be deployed last decade.Source: ITU World Telecommunication/ICT Indicators database.The ITU has recently issued requirements for IMT-Advanced, which constitutes the official definition of 4G. Requirements include operation in up-to-40 MHz radio channels and extremely high spectral efficiency. The ITU recommends operation in upto-100 MHz radio channels and peak spectral efficiency of 15 bps/Hz, resulting in a theoretical throughput rate of 1.5 Gbps. Previous to the publication of the requirements, 1 Gbps
was frequently cited as a 4G goal. No available technology meets these requirements yet. It will require new technologies such as LTE-Advanced (with work already underway) and IEEE 802.16m. Some have tried to label current versions of WiMAX and LTE as “4G”, but this is only accurate to the extent that such designation refers to the general approach or platform that will be enhanced to meet the 4G requirements. With WiMAX and HSPA significantly outperforming 3G requirements, calling these technologies 3G clearly does not give them full credit, as they are a generation beyond current technologies in capability. But calling them 4G is not correct. Unfortunately, the generational labels do not properly capture the scope of available technologies and have resulted in some amount omarket confusion.
Interleave-division multiple access
In DS-CDMA, distinct data streams dm are distinguished by different spreading sequences. Forward error correction (FEC) coding is typically done before interleaving and spreading, as shown in the upper part of Fig.1. Hence, interleaving is performed on a symbol-by-symbol basis. Conventionally, the same FEC encoder and the same interleaver is used for all data streams dm.
Extensions of Pure IDMA
The error performance of IDMA can be improved by means of orthogonal code-division multiplexing/ interleave-division multiple access (OCDM/IDMA). This optional extension of IDMA is depicted in Fig. 3. The data stream of one user is transmitted via Gm parallel layers. Orthogonal codes are used for the parallel layers. All layers of one user share the same interleaver. It is also possible to perform the spreading over multiple sub-carriers to obtain an MC-IDMA system. This is an interesting alternative to IDMA for systems with a huge number of sub-carriers, or an extension of existing or planned MC-CDMA systems.
Soft Link Adaptation
One enormous advantage of the low-cost IDMA-receiver is the inherent output of reliability information, Besides of delivering hard decisions after the final iteration, the receiver in Fig. 3 calculates estimates of the BER in an evaluation module. The evaluation module compares the estimated BER with a predefined target BER, Pt. Since the BER degrades with increasing number of layers because of increased multi-layer interference, the number of layers transmitted in the next block is decreased at the transmitter side if the estimated BER is higher than the target BER. If the estimated BER is below the target BER, the transmission power can be reduced. The proposed iterative receiver is appropriate for the suggested adaptation strategy. A large variety of data rates can be supported by the multi-code technique. As opposed to conventional adaptive modulation/channel coding techniques, the modulation scheme is fixed (and even binary) and the same channel code is used for all layers. Power adaptation/savings are particularly useful for the uplink.
High Bandwidth and Power Efficiency
Without adaptive power allocation a spectral efficiency of about 3.75 bits/Hz can be reached for one transmit antenna. With adaptive power allocation, a spectral efficiency of up to 8 bits/Hz (corresponding to 256QAM) for one transmitter antenna has been reported. With the parameters given in Table I, the maximum theoretic throughput for a single antenna system is 122.95 Mbps for a bit load of 3.75 bits/Hz, which is higher than the results presented for the uplink. In conjunction with the proposed adaptation strategy, a continuous operation near the theoretical limit can be achieved. However, due to soft link power adaptation the mobile device always uses minimum power for transmission what results in long battery life.
Pilot Aided Channel Estimation
The receiver under investigation needs reliable channel estimates. In IDMA it is suitable to use pilot-layer aided channel estimation where one layer for every user carries training symbols for channel estimation. This is especially useful for the uplink as the channel for every mobile station is different at a base station. An allocation of a pilot layer has been shown to achieve good estimates for the whole block length even for rapidly changing frequency-selective fading channels.
[attachment=21723]
. Introduction
The last few years have witnessed a phenomenal growth in the wireless industry, both in terms of mobile technology and its subscribers. There has been a clear shift from fixed to mobile cellular telephony, especially since the turn of the century.By the end of 2010, there were over four times more mobile cellular subscriptions than fixed telephone lines Both the mobile network operators and vendors have felt the importance of efficient networks with equally efficient design.This resulted in Network Planning and optimization related services coming in to sharp focus.With all the technological advances, and the simultaneous existence of the 2G, 2.5G and 3G networks, the impact of services on network efficiency have become even more critical. Many more designing scenarios have developed with not only 2G networks but also with the evolution of 2G to 2.5G or even to 3G networks. Along with this, inter-operability of the networks has to be considered.1G refers to analog cellular technologies; it became available in the 1980s. 2G denotes initial digital systems, introducing services such as short messaging and lower speed data. CDMA2000 1xRTT and GSM are the primary 2G technologies, although CDMA2000 1xRTT is sometimes called a 3G technology because it meets the 144 kbps mobile throughput requirement. EDGE, however, also meets this requirement. 2G technologies became available in the 1990s. 3G requirements were specified by the ITU as part of the International Mobile Telephone 2000 (IMT-2000) project, for which digital networks had to provide 144 kbps of throughput at mobile speeds, 384
kbps at pedestrian speeds, and 2 Mbps in indoor environments. UMTS-HSPA and CDMA2000 EV-DO are the primary 3G technologies, although recently WiMAX was also designated as an official 3G technology. 3G technologies began to be deployed last decade.Source: ITU World Telecommunication/ICT Indicators database.The ITU has recently issued requirements for IMT-Advanced, which constitutes the official definition of 4G. Requirements include operation in up-to-40 MHz radio channels and extremely high spectral efficiency. The ITU recommends operation in upto-100 MHz radio channels and peak spectral efficiency of 15 bps/Hz, resulting in a theoretical throughput rate of 1.5 Gbps. Previous to the publication of the requirements, 1 Gbps
was frequently cited as a 4G goal. No available technology meets these requirements yet. It will require new technologies such as LTE-Advanced (with work already underway) and IEEE 802.16m. Some have tried to label current versions of WiMAX and LTE as “4G”, but this is only accurate to the extent that such designation refers to the general approach or platform that will be enhanced to meet the 4G requirements. With WiMAX and HSPA significantly outperforming 3G requirements, calling these technologies 3G clearly does not give them full credit, as they are a generation beyond current technologies in capability. But calling them 4G is not correct. Unfortunately, the generational labels do not properly capture the scope of available technologies and have resulted in some amount omarket confusion.
Interleave-division multiple access
In DS-CDMA, distinct data streams dm are distinguished by different spreading sequences. Forward error correction (FEC) coding is typically done before interleaving and spreading, as shown in the upper part of Fig.1. Hence, interleaving is performed on a symbol-by-symbol basis. Conventionally, the same FEC encoder and the same interleaver is used for all data streams dm.
Extensions of Pure IDMA
The error performance of IDMA can be improved by means of orthogonal code-division multiplexing/ interleave-division multiple access (OCDM/IDMA). This optional extension of IDMA is depicted in Fig. 3. The data stream of one user is transmitted via Gm parallel layers. Orthogonal codes are used for the parallel layers. All layers of one user share the same interleaver. It is also possible to perform the spreading over multiple sub-carriers to obtain an MC-IDMA system. This is an interesting alternative to IDMA for systems with a huge number of sub-carriers, or an extension of existing or planned MC-CDMA systems.
Soft Link Adaptation
One enormous advantage of the low-cost IDMA-receiver is the inherent output of reliability information, Besides of delivering hard decisions after the final iteration, the receiver in Fig. 3 calculates estimates of the BER in an evaluation module. The evaluation module compares the estimated BER with a predefined target BER, Pt. Since the BER degrades with increasing number of layers because of increased multi-layer interference, the number of layers transmitted in the next block is decreased at the transmitter side if the estimated BER is higher than the target BER. If the estimated BER is below the target BER, the transmission power can be reduced. The proposed iterative receiver is appropriate for the suggested adaptation strategy. A large variety of data rates can be supported by the multi-code technique. As opposed to conventional adaptive modulation/channel coding techniques, the modulation scheme is fixed (and even binary) and the same channel code is used for all layers. Power adaptation/savings are particularly useful for the uplink.
High Bandwidth and Power Efficiency
Without adaptive power allocation a spectral efficiency of about 3.75 bits/Hz can be reached for one transmit antenna. With adaptive power allocation, a spectral efficiency of up to 8 bits/Hz (corresponding to 256QAM) for one transmitter antenna has been reported. With the parameters given in Table I, the maximum theoretic throughput for a single antenna system is 122.95 Mbps for a bit load of 3.75 bits/Hz, which is higher than the results presented for the uplink. In conjunction with the proposed adaptation strategy, a continuous operation near the theoretical limit can be achieved. However, due to soft link power adaptation the mobile device always uses minimum power for transmission what results in long battery life.
Pilot Aided Channel Estimation
The receiver under investigation needs reliable channel estimates. In IDMA it is suitable to use pilot-layer aided channel estimation where one layer for every user carries training symbols for channel estimation. This is especially useful for the uplink as the channel for every mobile station is different at a base station. An allocation of a pilot layer has been shown to achieve good estimates for the whole block length even for rapidly changing frequency-selective fading channels.