WIRELESS BROADBAND NETWORK WIMAX AND 3G Showing newest 22 of 62 posts from 02/01/2008 - 03/01/2008. Show older posts Showing newest 22 of 62 posts from 02/01/2008 - 03/01/2008. Show older posts WIMAX TRANSMIT POWER CALCULATION Do we need to consider return loss of the device along with insertion loss when we calculate the output power of the particular device? For example Balun has return loss of 12dB and IL of 2.5 dB, when i give input to the balun as 0dBm what will be the out put of the balun power available? output power= Input power-IL or output power= Input power-(IL+RL)? In such case if the input to the BALUN is 0dBm then the output of the Balun will be - 15dBm because of the return loss 12 dB and insertion loss 2.6dB, Is this calculation correct? If there is really a 12 dB return loss in the balun then the calculation is correct. Iam just wondering why the RL of the Balun is 12dB. I think it is quite large. We use balun to match impedance and minimize RL. Can you tell how the value of RL obtained? Do not consider the return loss when making your link budget or EIRP calculations. The insersion loss is to be considered (only). The return loss is the indicator of the health of your cable and antenna together. The antenna is an impedence matching device from the cable (50 ohms) to free space (377 ohms) and is frequency dependant. Since there is no perfect impedence match there will be some reflected power. A return loss of 13 db means that 1/20 th of the power was reflected. If you were transmitting 10 watts than .5 watts was refected. This number is too little to worry about. However, if you see reflected power start to rise you must ceck your cable and antenna and jumpers. i over looked return loss as loss due to return instead of loss of the return. thats why i think its value is high for a loss. to consider it theoretically in your calculation. just subtract the linear value of RL form 1 then convert it back to dB for 12dB RL means 1/16 of incident is reflected hence 15/16 is for the load (1-1/16) So your loss due to return is 10log(15/16)= - 0.28dB [get this widget] Read More... IMPORTANCE OF THE TR ANSMITTIG ANTENNA GA IN FOR THE BASE STATION As per my RF design i am getting +40dBm Tx power at the antenna port after subctracting the insertion loss and Returm loss of Balun and TDD switch, the same Power(+40dBm)is fed to TX directional antenna, My Question is ,Will the TX Antenna gain(G) would help to increase radiated power more than 42dBm? Please help me in understanding more on the inportance of antenna Gain(G)? Forward power consists of transmit power minus cable and connector loss, minus combiner loss (if applicable) plus atnenna gain (in dbi) = EIRP Example: 20 Watts = +43 dbm - 3 db cable loss = +40 dbm, plus 15 dbi of antenna gain = +55 dbm EIRP http://www.satcom.co.uk/article.asp?article=21 [get this widget] Read More... WIMAX RECEIVER SENSITIVITY I have some problem to understand the Sensitivity Calcutaion in IEEE 802.16e-2005. For the OFDM PHY, at page 351 of the standard (Receiver Requirements), the sensitivity is scaled by the number of active subchannel (for example in downlink i can use only one among 16 channels). In the OFDMA part (page 646, Receiver sensitivity) in the expression appear Nused*(Fs/Nfft), where I understand that Nused are all subcarrier except DC subcarrier. So, there is a difference in the calculation. For the OFDMA the expression rapresent the minimum received power that guaranted a BER of 10^-6, in the case of the end user in uplink used all the available channels. This is the worse case, infact the subcanalization has the following advantage: 1) the trasmitter power is concentrated in a limited bandwidth, so this can increase the coverage 2) the Bandwith, in the expression of sensitivity, is smaller, so the minimum received power is less that in the case of all sub-channel allocated to one user. Can anyone explain me the difference? Receiver sensitivity is a factor of bandwidth as follows: Receiver sensitivity = -174 + 10log BW + NF of receive amp so, the narrower the bandwidth the lower the noise, hense the lower the receive thereshold for narrower BW. The Standard 802.16e (I refer to OFDMA) specify: Rss=-114+ SNRrx - 10log(Repetition Factor) + 10log( FS x Nused / Nfft) + ImpLoss + NF Where, in according to the definition of "Nused", the term "Fs x Nused / Nfft" is practicaly the bandwidth occupied by all sub-channels. So, this is the minimum sensitivity for a user that use all available subchannels (in OFDMA). But if a MS use only one subchannel, the BW is narrow hense the receive thereshold is lower. If I use this expression for sensitivity calculation I have the worst case results, because the expression don't take in account the effect of subchanalization. Is this true? Maybe, I think I can take in account the canalizazion effect as a Gain in the link budget (One gain for the power concentration in a sub-channel, and one gain to compensate the fact that the sensitivity, in reality, is better). But my problem is: "how can I foreseen the canalization gain if I don't know how many sub-channels the scheduler of the BS allocate for each user?" Download the 802.16e standard (if you haven't already) and do a "find" on the key words "Link Budget". You will find your answers here. I started to try to describe Link Budgets and Path Balance but they do a better job than I do. "Receiver sensitivity = -174 + 10log BW + NF of receive amp" What's NF? Is this equation valid for single carrier modulation? -174 is the thermal noise floor, 10log BW applies to bandwidths, run a couple of exercises, try 200 khz, then 1.25 Mhz then 5 Mhz, etc. NF is the noise figure of the receive amp. BTS amps run around 5-7 db, smaller cellphone amps run higher. Receiver threshold is the amount of receive signal required to obtain a certain throughput at 1 x 10-6 What about this equation Rss= SNR-10log(BW/Rb) + Nw +Nf Nw:thermal noise floor ; Rb: data rate (b/s) is it equivalent, there is an extra term (SNR+logRb). An other question: the required SNR have to be calculated or is given, what's the formula if yes? The signal part of the equation depends on the strength of the recieve signal. The noise part is dependent of the bandwidth of the receive filter. The next factor to understand is the interference, because the determining factor for throughput will be decide by the type of modulation and coding, and that is determined by the Signal to Noise + Interference sometimes written CINR for Carrier to Interference & Noise Ratio or C/N+I. I was referred to this equation just to have relation between the range and the throughput, actually I forgot the source. Also I‘m working with the following formula: Rss=-174+10 log(BW(Hz))+SNR+NF+10log(Nsubchannels) Referring to an example of BL attached. Also I use these values of SNR: Modulation coding rate SNR Rx BPSK ½ 6.4 QPSK ½ 9.4 QPSK ¾ 11.2 16-QAM ½ 16.4 16-QAM ¾ 18.2 64-QAM 2/3 22.7 64-QAM ¾ 24.4 Are those values valid for all bandwidths (exactly 25MHz)? Other question, what are the typical values of antenna gain? directive=17 dBi; omnidirectionnel=0 dBi what about sectoriel? [get this widget] Read More... MODULATION Dear Friends, Can any one share the info about the ideal values of CINR and RSSI vaule at different bandwidth and modulation. Bandwith : 3 , 3.5 ,6 6.5 MHz Modulation : BPSK ½ QPSK ½ QPSK ¾ QAM 16 ½ QAM 16 ¾ QAM 64 2/3 QAM 64 ¾ please note that the values differ from vendor to fendor. The following table referes to a 3.5MHz BW System: Typical levels for BER <1x10-6 are given. Modulation / FEC / Rx Sensitivity / CINR 64QAM 3/4 -80.0dBm 23.0dB 64QAM 2/3 -82.0dBm 21.0dB 16QAM 3/4 -86.0dBm 17.0dB 16QAM 1/2 -88.0dBm 15.0dB QPSK 3/4 -92.0dBm 11.0dB QPSK 1/2 -94.0dBm 9.0dB BPSK 1/2 -98.0dBm 5.0dB these values are for BER <1x10 E-6, and they tend to produce a packet loss of about 1x10 E-2 which is fine for TCP, but a murder for UDP/RTP multimedia. Also, consider faster scheduling types in case multimedia is a key role of your network. Check for performance with short packets - ther may be some surprises with latencies and throughput ;) This information is provided by the vendor. The vendor will provide a minimum signal strength to achieve each modulation/coding scheme. The noisie floor is dependant of the bandwidth (-174 + 10logBW/hz) plus the Noise Figure of the receive amplifier. The NF will vary by vendor and will also vary if set at the top of the tower (close to the antenna) or on the ground (typically in the base station). Frequency reuse will increase the signal strength requirement (S/N+I) [get this widget] Read More... FREQUENCY PLANNING Which is the best plan for frequency reuse in wimax.