Wimax standards and Security The Wimax

TABLE 5.1
Path Loss Exponent (n) and Log-Normal Shadowing Standard Deviation (σ, in dB)

Source	Frequency (GHz)	Path Loss Exponent n	σ (dB)	Comments
Seidel [23]	0.9	2.8	9.6	Suburban (Stuttgart)
Erceg [13]	1.9	4.0	9.6	Terrain-category B
Feuerstein [24]	1.9	2.6	7.7	Medium antenna height
Abhayawardhana [25]	3.5	2.13	6.7–10	Ref. 25, tables 2 and 3
Durgin [26]	5.8	2.93	7.85	Ref. 26, figure 7,
Porter [27]	3.7	3.2	9.5	residential Some denser urban
Rautiainen [28]	5.3	4.0	6.1	Ref. 28, figures 3 and 4
Schwengler [29]	5.8	2.0	6.9	LOS
	5.8	3.5	9.5	NLOS
	3.5	2.7	11.7	See Section 5.3.4
Average	3.5–5.8	3.0	8.7

Summary of values for various frequencies reported for suburban or residential areas.
TABLE 5.2

Parameter	Unit	Equation	BPSK 1/2	64QAM 3/4
Data rate	Mbps	r	1.4	12.7
Subscriber Tx power	dBm	A	23.0	23.0
Subscriber antenna gain	dBi	B	18.0	18.0
Subscriber cable loss	dB	C	0.0	0.0
Transmitted EIRP Base Rx antenna gain Base cable loss Thermal noise Channel width Thermal noise in channel Base noise figure Base noise floor	dBm dBi dB dBm/Hz MHz dBm dB dBm/Hz	D = A + B − C F 10 × log(kT) + 30 H = 10 × log(kTG) + 90 J = H + I	41.0 17.0 1.0 −174.0 −108.6 −104.6	41.0 17.0 1.0 −174.0 3.5 −108.6 4.0 −104.6
SNR required Receiver interference margin Base Rx sensitivity Diversity gain Total System gain Log-normal fading std dev Log-normal fade margin Building penetration loss Maximum reverse path loss	dB dB dBm dB dB dB dB dB dB	K L M = J + K + L Q = D + E − F − M + N σ O P R = D + E − F − M +	6.4 0.0 −98.2 155.2 9.6 12.3 0.0 142.9	24.4 0.0 −80.2 0.0 137.2 9.6 12.3 0.0 124.9

WiMAX Reverse Link Budget at 3.5 GHz, for 3.5 MHz Channels, in Different Modulations (BPSK to 64QAM)


E
G 3.5
I 4.0
N 0.0
N − O − P


TABLE 5.3
WiMAX Reverse Link Budget at 5.8 GHz, for 10 MHz Channels, in Different Modulations (BPSK to 64QAM)
Parameter Unit Equation BPSK 1/2 64QAM 3/4

Data rate Mbps r 2.0 18.2

Subscriber Tx power dBm A 18.0 18.0
Subscriber antenna gain dBi B 16.0 16.0
Subscriber cable loss dB C 0.0 0.0

= + −
Transmitted EIRP dBm D A B C 34.0 34.0
Base Rx antenna gain dBi E 16.0 16.0
Base cable loss dB F 1.0 1.0

× + − −
Thermal noise dBm/Hz 10 log(kT) 30 174.0 174.0
Channel width MHz G 10.0 10.0

= × + − −
Thermal noise in channel dBm H 10 log(kTG) 90 104.0 104.0
Base noise figure dB I 4.0 4.0

= + − −
Base noise floor dBm/Hz J H I 100.0 100.0
SNR required dB K 6.4 24.4
Receiver interference margin dB L 0.0 0.0

= + + − −
Base Rx sensitivity dBm M J K L 93.6 75.6
Diversity gain dB N 0.0 0.0
Total system gain dB Q = D + E − F − M + N 142.6 124.6
Log-normal fading std dev dB σ 9.6 9.6
Log-normal fade margin dB O 12.3 12.3
Building penetration loss dB P 0.0 0.0
Maximum reverse path loss dB R = D + E − F − M + 130.3 112.3
N − O − P
We summarize parameters for licensed radio systems at 3.5 GHz with the link budget shown in Table 5.2.
Link budgets in unlicensed bands are similar to the above but are usually limited by a lower maximum allowed EIRP as shown in Table 5.3.

5. 
   In-Building Penetration
   

Fixed wireless service may use antennas placed on individual homes, but that comes with a number of obvious problems: customers may not welcome structures on their homes, and installation time and cost are high. The holy grail of wireless access consists in shipping a small device, like ADSL or cable modem, that customers may install without on-site technician time. Furthermore, the clear advantage of wireless data services lies in its portability or full mobility; therefore it seems clear that the trend is to pursue small indoor devices. Unfortunately, sending RF signal into buildings comes at an additional cost that can be quantified by an additional building penetration loss in the link budget.
Measurement campaigns show once again that the distribution is close to log-normal [20]. A Gaussian function is a good approximation of the cumu- lative distribution function (CDF) of indoor measurements, as plotted in


100%
80%

CDF
60%
40%
20%
0%
0 5 10 15 20 25 30 35
dB loss


FIGURE 5.1
Penetration loss into residential buildings, cumulative density distribution, and Gaussian approximation for 1900 and 5800 MHz.


Figure 5.1. The mean and standard deviations of indoor penetration loss vary with frequency, types of homes, and environment around the homes. Varia- tions also depend on the location within the building (near an outside wall, a window, or further inside). Finally, the angle of incidence with the outside wall also has a significant impact [30]. Precise characterization of in-building penetration is therefore difficult. Nonetheless, an approximation of an aver- age penetration loss µ_i around 12–15 dB and a standard deviation σ_i between 5 and 8 dB seems to be the norm in published studies [26,31,32]. Table 5.4 summarizes some published results for residential homes.

=

= =
Many similar studies are available for university or industrial campuses as well as high-rises, but these values are typically higher than for residential homes. They also depend heavily on the floor, height of neighboring build- ings, or clutter. Let us limit our analysis to residential and suburban areas. Few measurements are available at 3.5 GHz. The review of fairly large data collection campaigns at 1.9, 2.5, and 5.8 GHz [29–33], as well as personal measurements are summarized in Figure 5.1 and in Table 5.4. These results lead us to choose empirical values of µ_i 12 dB at 3.5 GHz, µ_i 15 dB at
5.8 GHz, and σ_i 6 dB in both cases.

i

,
With that in mind, we consider that in-building penetration is a log-normal random variate independent of the large-scale shadowing. Therefore, the log-normal fading used for indoor propagation should be the normal random
variable N(µ_i, σ² + σ²). Both median penetration loss and modified excess margin should be taken into account for a new indoor link budget.


TABLE 5.4
Penetration Loss into Residential Buildings: Median Loss (µ_i) and Standard Deviation (σ_i) from Experimental Results Reported at Various Frequencies
Source Frequency (GHz) µ_i (dB) σ_i (dB) Comments

Aguirre [31]	1.9		11.6		7.0	Ref. 31, figure 3
	5.9		16.1		9.0
Durgin [26]	5.8		14.9		5.6	Ref. 26, table 5 average
Martijn [32]	1.8		12.0		4.0	Ref. 32, table 1
Oestges [30]	2.5		12.3		–	Ref. 30, table 6 (avg. Le + L^rge)
Schwengler Schwengler [29]	1.9 5.8		12.0 14.7		6.0 Personal measurements 5.5 Ref. 29, table 2
Average	≈2		12.0		5.7
5.8		15.2		6.7

TABLE 5.5

Data rate	Mbps	r	1.4	12.7
Subscriber Tx power	dBm	A	23.0	23.0
Subscriber antenna gain	dBi	B	18.0	18.0
Subscriber cable loss	dB	C	0.0	0.0
Transmitted EIRP	dBm	D = A + B − C	41.0	41.0

WiMAX Reverse Link Budget at 3.5 GHz into Residential Buildings, for 3.5 MHz Channels, in Different Modulations (BPSK to 64QAM)
Parameter Unit Equation BPSK 1/2 64QAM 3/4

Base Rx antenna gain dBi E 17.0 17.0

Base cable loss dB F 1.0 1.0

× + − −
Thermal noise dBm/Hz 10 log(kT) 30 174.0 174.0
Channel width MHz G 3.5 3.5

= × + − −
Thermal noise in channel dBm H 10 log(kTG) 90 108.6 108.6
Base noise figure dB I 4.0 4.0

= + − −
Base noise floor dBm/Hz J H I 104.6 104.6
SNR required dB K 6.4 24.4
Receiver interference margin dB L 0.0 0.0

= + + − −
Base Rx sensitivity dBm M J K L 98.2 80.2
Diversity gain dB N 12.0 12.0
Total system gain dB Q = D + E − F − M + N 167.2 149.2

i
Combined log-normal std dev dB ,σ² + σ²
11.3 11.3

Log-normal Fade Margin dB O 14.4 14.4
Building Penetration Loss dB P 12.0 12.0
Maximum Reverse Path Loss dB Q = D + E − F − M + 140.8 122.8
N − O − P

This has a significant impact on the total link budget—see Table 5.5. In fact, some manufacturers even claim that indoor devices are impractical in unlicensed bands, which would lead to too small a radii of coverage in the lim- ited unlicensed power levels. In licensed bands as well, even though higher

transmit power is allowed, indoor radio units need to somehow increase their link budgets: advanced diversity schemes with a plurality of antennas are usually used. Some WiMAX systems also have the ability to use sub- channel groups with a dynamic number of subcarriers; link budget may then be increased by providing full power to that group (at the cost of overall throughput).

That same argument may be made for unlicensed frequencies as well; advanced diversity combining schemes and MIMO may be enough to com- pensate for high penetration losses as well as for the low transmit powers allowed [34].

3.