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QoS Improving in Poor Radio Coverage Area Disclosure Number: IPCOM000005359D
Original Publication Date: 2001-Aug-31
Included in the Prior Art Database: 2001-Aug-31
Document File: 5 page(s) / 44K

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QoS Improving in Poor Radio Coverage Area

This text was extracted from a WORD97 document.
This is the abbreviated version, containing approximately 52% of the total text.

QoS Improving in Poor Radio Coverage Area


It is known that the signal power received from the serving Base Stations (BSs) in a CDMA cellular network is not uniformly distributed in the cell area. Basically, close to the BSs there is enough power and codes available, while farther, close to the border area, power strength decreases, which might generate poor radio coverage areas. The QoS, consequently, depends strongly on the user's positioning.

As a consequence, in poor radio coverage, more calls will be blocked and more connections will be dropped due to limited power budget to compensate for the power attenuation. Therefore the call drop risk, even for high priority calls, is high in the poor coverage area.

Figure 1 shows the evolution of the BS dedicated power level per radio link with a mobile station's (MS) distance from BS (distance BS-MS) in an UMTS environment. It is observed that the power level depends strongly on the distance BS-MS. Results were collected from a large cellular network (37 macro-cells) wrapped-around with cell radius 1 Km. Radio parameters were compliant with 3GPP specifications [1]: Maximal Total Tx Power at BS 43 dBm (Tx stands for transmitted), Maximal BS Tx Power per MS 30 dBm, power control step size 2 dB.

The power result presented below is for a speech service, which has the following characteristics: bit rate 8kbit/s, coding factor 0.35, spreading factor 128, processing gain 25.25 dB, Eb/No 7.9 dB.

The power control algorithm is Signal to Interference (SIR)/or Carrier to Interference (C/I) ratio based, aiming to give each user the same quality of signal, or in other words, the same SIR for a given application.

Known techniques can improve access in poor coverage area by limiting the acceptance in good coverage areas to lower capacity thresholds. This is because the power budget is common and provisioning of some power is possible if other concurrent users reduce their "power occupancy". Such techniques are difficult to implement in an effective way: reducing the power credit in good coverage area will inherently reduce the overall carried traffic, since blocking and even call dropping will be increased in good coverage areas.

Simulation scenarios allow one to observe that a high proportion of users are prevented from connecting to the system due to the power limitation set by the network. Indeed, the actual UMTS standard imposes the same maximum power limitation regardless of user's positioning or various user's power needs [1]. This is more damaging in a context with various levels of calls priorities.

A user is considered interfered if its C/I does not reach the target C/I. Full loading accounts for 5% of interfered users (or 5% outage). At full loading, the two limitations preventing the further increase of MS dedicated power are:

The power level emitted by the B...