ABSTRACT
of the Master's Qualification Work
“Features Reseach and Methodology Developent of New Generation Networks Building
for Mobile Operators”
Content
Introduction
1. A them urgency
2. The purpose and problems of the development
2.1 The work purpose
2.2 The main problems of the development
3. Prospective scientific novelty of the received results
4. The review of developments and researches on a theme
5. The description of the received and planned results of work
5.1 Uplink channel budget analysis and area coverage definition
5.2 Uplink channel loading
5.3 Downlink channel loading
5.4 Downlink area coverage analysis
Conclusions
Bibliography
Note
Introduction
High requirements for informatization of all spheres of human activity led to the need for access to information resources not only at home and in the office, but also in public places. As a result, competition between traditional telephone services and data services started. This revolutionary transition from voice traffic to data traffic is base on the NGN (Next Generation Network) ideology, which has greatly influenced the organization of networks[1].
The concept NGN refers to a heterogeneous multi-service network that ensures the transfer of all types of media traffic, and provides a distributed unlimited range of telecommunications services with the possibility of adding, editing and distributed billing. The network supports the transfer of traffic with different requirements for quality of service and provides support for these claims.
Thus, the deployment of NGN network will satisfy the interests of customers - consumers and operators alike. The first will receive a new wide range of services that meets the content and quality, and the second - opportunities to upgrade the network and, as a consequence, new trump card for the expansion of subscriber base. It is particularly important for the mobile operator does not miss a moment of transition, because the user requirements for mobility are growing with each passing day.
1. A them urgency
The main problem in introducing new services for mobile operators is that the existing GSM networks were built on circuit-switched technology and now unable to provide a wide range of services to meet consumer demand. The introduction and use of GPRS / EDGE technology is not a solution, because not ensure the necessary quality parameters for most modern services.
Upgrading networks and introduction of new technologies can be a solution, in particular the transition to the mobile networks of third generation (3G).
Third generation mobile network are the result of the implementation of the concept of International Mobile Telecommunications-2000, IMT-2000. It is based on the idea of creating a new generation family of mobile communication systems covering the wireless access technology, terrestrial wireless and satellite communications [2]. The work on standardizing the interfaces of the IMT-2000 family is now completed and includes 5 radio interfaces in its composition: IMT-DS (basic technology is a WCDMA), IMT-MC (cdma2000), IMT-TC (TD-SCDMA), IMT-SC ( UWC-136), IMT-FT (DECT EP).
In Europe, the idea of IMT-2000 is implemented as a concept of Universal Mobile Telecommunications System, UMTS. Диапазон возможностей и областей применения данной системы необычайно широк: в ней предлагается широкий спектр услуг по высококачественной передаче речи, данных, мультимедийных сервисов. UMTS allows to organize a full interaction with the systems of GSM.
Code division of channels is used in the UMTS system in the digital broadband air interface, covering the Internet, multimedia and other high capacity applications. It is Wideband Code Division Multiple Access, WCDMA.
Maintaining and expanding mobile operator subscriber base through the provision of new services by the introduction of next-generation communications networks is the work purpose.
Mobile telecommunications network is the object of development
Method of new generation networks construction by mobile operators is the subject of development.
2.2 The main problems of the development
Upgrading a 2,5 Generation mobile communications network problems at the level of management, transport and access must be addressed in the process of writing the work to enable the provision of advanced mobile services in compliance with their quality.
3. Prospective scientific novelty of the received results
Scientific novelty of the master's work results lies in the proposed method of transition to next generation networks by mobile operators. The method is an upgrade algorithm for 2,5 Generation mobile network, which is also considered the optimizing procedure for the radio access network.
4. The review of developments and researches on a theme
Researches and developments on the subject were started in the late 90-ies. The first steps in this area were standards developments for third generation mobile networks [3]. Since 1998, these studies were concentrated in the partnership project 3GPP with ETSI [4].
Building a UMTS network research issues conducted by research teams of developers of telecommunications equipment actively, such as Alcatel, Nokia, Siemens, etc.
a number of scientists engaged in a new generation mobile networks research at the CIS. A large proportion of their work is devoted to designing and optimizing the radio access sub-networks. It is worth recalling the work of Smolovik “Methods for planning and optimization of radio subsystem for UMTS Network”, Aksenov “The influence of handover procedures on the quality of services in networks of UMTS”, Babin “Designing an optimal radio network subsystem 3G/UMTS/WCDMA based on the theory of monotone systems”, Veduta “Optimizing digital communication systems with a channel code”, etc.
5. The description of the received and planned results of work
Uplink and downlink parameters of radio UMTS network were investigated in the course of this work, their impact on the cells capacity and coverage area. Since UMTS network can operate in asynchronous mode, the channel parameters considered independently of each other.
5.1 Uplink channel budget analysis and
area coverage definition
Uplink budget analysis can get the value of allowable losses (in dB) on the radio path from the subscriber mobile terminal to the base station. It is necessary to consider some special parameters. These include the supply noise immunity, the stock of rapid fading, the gain in soft handover [5].
The values of path loss can be used to determine the service area. Effective service area of WCDMA is defined by the average cell area to the site in km2/site for pre-defined standard medium of distribution and the supported density of traffic.
The distance to the cell borders R can be calculated from the known distribution model. For example, the Okumura-Hata model, which describes the average propagation variant and allows to convert the maximum allowable transmission loss in dB in the maximum range to the cell borders in kilometers, given the values of the carrier signal frequency, and the height of the BS and MS antennas.
Okumura-Hata equation has the form:
 |
(5.1) |
where
Lp — allowable path loss, dB;
ƒ — carrier frequency, MHz;
hb и hm — height of the BS and MS antennas, m;
a(ƒ, hm) — MS antenna gain function of the height and the carrier frequency;
R — distance from MS to BS, km.
Options A and B have different values for different frequency range. So for the range 150 - 1000 MHz, A = 69.5, B = 26.16, for the range of 1500 - 2000 MHz, A = 46.3, B = 33.9.
Parameter a(ƒ, hm) The parameter is defined in different ways depending on the type of settlement.
For medium and small towns:
 |
(5.2) |
For cities:
 |
(5.3) |
Based on the above analysis of the radiolink budget and distribution model it is possible to determine the distance R to the cell borders kilometers. Taking the height of the BS antenna 30 m and MS antenna height 1,5 m and carrier frequency of 1950 MHz, obtain:
 |
(5.4) |
Determined R from the expression above, it's possible to get the cell area, which is also a function of the configuration of partition in sectors:
 |
(5.5) |
The K values depend on the number of sectors that cell are divided and are presented in Tabl. 5.1
Table 5.1 - Dependence of coefficient K on the number of sectors
| The number of sectors in a cell |
1 |
2 |
3 |
6 |
| K value |
2,6 |
1,3 |
1,95 |
2,6 |
After determining the covered area by one cell, it is necessary to estimate the traffic that is available in this cell. When the frequency reuse WCDMA system is 1, the system is usually limited by interference by air interface, and, thus, necessary to calculate the magnitude of interference and capacity of the cell.
5.2 Uplink channel loading
The uplink load factor is defined as
 |
(5.6) |
and allows to predict the noise magnitude excess of the thermal noise:
 |
(5.7) |
The Interference cruising in the link budget must be equal to the maximum acceptance of noise excess.
explanation of symbols and their recommended settings are shown in Tabl 5.2.
Table 5.2 - Main uplink parameters values
| |
Definition |
Recommended values |
| N |
Number of users per cell |
|
| υj |
The coefficient of the active user at the physical level |
0.67 for voice
1 for data |
| (Eb/N0)j |
Signal energy per bit, divided by the spectral noise density, which must meet the specified quality of service. Noise includes thermal noise and interference |
Depends on the service bit rate, channel with multipath fading, antenna diversity for reception, MS speed, etc. |
| W |
WCDMA Cheap rate |
3.84 МCheap/с |
| Rj |
j user bit rate |
Depends on service |
| i |
The ratio of interference levels from other cell to own cell interference, which is determined by the BS receiver |
Macrocell with omnidirectional antenna: 55% |
Fig. 5.1 shows the capacity dependence from the noise level in the uplink. When calculating the assumptions taken (Eb/N0)j = 1.5 dB и i = 0.65. The full cell capacity for all concurrent users is displayed instead of the users number.
Figure 5.1 - Cell capacity dependence from noise
5.3 Downlink channel loading
Downlink load factor can be determined by basing on similar principles as for the uplink, although the parameters are some different:
 |
(5.8) |
Compared with the uplink load equation the most important new parameter is α, which represents the orthogonality factor in downlink. WCDMA uses orthogonal codes in the downlink to separate users. Orthogonality, equal to 1 corresponds to the ideal orthogonal users. Usually, the orthogonality in multipath channels is from 0,4 to 0,9.
Effect of antenna diversity in transmission should be included in the required ratio (Eb/N0). Downlink load factor is similar to the uplink one in the sense that when it approaches to 1 a system reaches its full capacity [6].
To specify the coverage is important to estimate the total required power amount of BS transfer in the downlink. It should be based on the average transmission power for the user, rather than the maximum power transfer to the edge of the cell, as shown in the radio link budget.
The minimum required transmit power for each user defined by the average attenuation between the transmitter and the mobile receiver and the MS receiver sensitivity in the absence of interference in multiple access (within or between cells). Then the effect of increasing the interference is added to this minimum power and total power is the transmit power required for the user, who is in 'average' location in the cell. Mathematically, the total transmit power can be represented by the following equation:
 |
(5.9) |
where
Nrf – spectral density of noise in the input stage of MS receiver. This parameter can be obtained from
 |
(5.10) |
where NF – MS receiver noise figure with typical values of 5 - 9 dB.
Load factor may be approximated by its average value:
 |
(5.11) |
Fig. 5.2 shows the downlink capacity (Kbps) dependence from the maximum allowable path loss (dB) at different transmitter power BS (10 and 20 W). As can be seen from the figure, the increase of power by 100% gives a very small gain in capacity, and thus is ineffective. More correct is the division of power in the downlink between the two carriers, but this method requires that the frequency distribution allows the operator to use two carriers at the BS [7].
Figure 5.2 - Downlink capacity research
5.4 Downlink area coverage analysis
Downlink service area depends on the load more than the uplink one. This occurs because the maximum downlink transmission power remains the constant - the same 10 watts are shared regardless of the number of users, whereas each additional user has its own amplifier in the uplink. Therefore, even at low load in the downlink service area decreases as the number of users is increased (Fig. 5.3).
Figure 5.3 – Coverage area decreasing with users number increasing
Animation consits of 7 frames with a 500 ms delay between ones;
delay before repeat is 1 s; number of cycles of playing is limited to 7
To investigate the dependence between downlink bandwidth and the radius of the cell the values were taken: (Eb/N0) = 2 dB, interference level from other cells 0.65, orthogonality 0.6. The research was conducted at two values of BS transmitter power10 W and 20 W. The result of the research is shown in Fig. 5.4
Figure 4 – Dependence between the cell radius and downlink bandwidth
It is worth noting that the value (Eb/N0) significantly affects the maximum downlink bandwidth. The ratio (Eb/N0) tends to decrease for high speed transmission. So (Eb/N0) = 5.5 dB at orthogonality 0.6 can get the full capacity of about 800 kbit/s/cell. And decrease of (Eb/N0) to 2dB may get the capacity of 1800 kbps/cell.
Another important feature is that the lower requirement for (Eb/N0), the lower power required to provide the same performance and the radius of the cell can be increased.
Conclusions
The following conclusions can be formulated as a result of the work:
По результатам проделанной работы можно сформулировать следующие выводы:
- service area can be determined using the model of radio wave propagation, such as Okumura-Hata, based on the channel budget data;
- the service area is defined by a range of uplink in macrocells, since the transmitter power of mobile station is much smaller than the base station transmitter power
- load factor can be used to predict the cell capacity. Since the uplink and downlink bandwidth may differ from each other in UMTS network, then the load factor is calculated separately for each channel;
- downlink capacity may limit the service area. If it is necessary to ensure reliable operation of services requiring high speed, it is necessary to decrease cell area and thereby increase their capacity.
Bibliography
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Note
When writing this abstract the master’s qualification work is not completed. Date of final completion of work: December, 1, 2010. Full text of the work and materials on a work theme can be received from the author or his scientific supervisor after that date.
