RE: stds-802-16-tg4: Need for RF input to TG4 PHY specs
Tal,
Thanks for the feedback. Some questions:
1) Does the EVM measurement method specified in 802.11a do what you are
asking for? Is there currently a way to take practical measurements for
OFDM signals? Would different test limits need to be created for the
differing data rates and OFDM modes?
2) A spectral mask helps minimize interference other like systems, but it
seems to me that a receiver adjacent channel rejection spec is also required
for the system design. This will ultimately define the channel filters for
the receiver and was also specified for 802.11a.
3) I have seen several vendors specifying Tx flatness very tightly and the
802.11a spec seems reasonable. If no spec is required, it would be fine by
me.
Drayt
-----Original Message-----
From: owner-stds-802-16-tg4@ieee.org
[mailto:owner-stds-802-16-tg4@ieee.org]On Behalf Of Tal Kaitz
Sent: Monday, May 07, 2001 8:33 AM
To: Stds-802-16-Tg4@Ieee. Org
Subject: RE: stds-802-16-tg4: Need for RF input to TG4 PHY specs
Hi all,
Some comments:
1. EVM is a good measure for all transmit impairments for the OFDM case:
PA non-linearities, Phase noise, group delay distortion. However it is
not-enough for OFDMA since the impairments caused by, say, a single SU will
distort other SUs using different sub-channels. Therefore we should define
an 'aggregate' EVM measurement which maybe the worst case distortion in all
subchannels, and all the subchannels are used.
2. We should define a spectral mask. This should take into account the
desired level of ACI.
3. Tx flatness is not critical to system performance in OFDM, and should not
be specified tightly.
Tal Kaitz
-----Original Message-----
From: Drayt Avera [mailto:davera@rf-solutions.com]
Sent: Thursday, May 03, 2001 5:17 PM
To: Stds-802-16-Tg4@Ieee. Org
Subject: stds-802-16-tg4: Need for RF input to TG4 PHY specs
TG4 Team,
Here are some items which need to be addressed in the TG4 spec. Let's get a
dialog started and try to solidify some numbers prior to the meeting in a
few weeks.
1) Need specs for the expected interference conditions or protection
requirements. In 802.11a minimal adjacent channel specs are specified, and
I would think we would need greater interference protection. Some possible
specs to add:
minimum adjacent channel protection (about 40dB?) vs channel bandwidth
selected
alternate adjacent channel protection
TBD MHz blocking (jamming protection)
max expected receiver level (in-band and out of band)
2) Transmit or receive linearity requirements should be specified. The
receiver linearity will impact the system design for near/far issues. On
the transmit side, maybe an EVM measurement under standard conditions
(similar to 802.11a) make more sense.
3) Need to determine a sensitivity requirement. Depending on the
interference and linearity requirements it should be around 5-6dB. What SNR
is required for the various modulation methods? I think a table of minimum
sensitivity vs channel bandwidth would be most appropriate.
4) Adjustment range for power control and any Rx AGC including response
characteristics and resolution. There were some previous responses showing
around 30-40dB, and it would be good to discuss the calculations that anyone
has done. 802.11a has requirements for the Tx flatness of +/-2dB.
5) Tx flatness: are the 802.11a requirements good enough?
6) Should we have a Clear Channel Assessment (CCA) type function and a
threshold to transmit?
7) TDD and FDD coexistence strategy. Are most of you are headed towards
TDD?
8) Phase noise requirement: Is this buried in the EVM measurement? It
would be simpler to specify it directly.
9) Are there any group delay requirements (absolute or variation)?
10) Some misc items need to be addressed:
temp range: same as 802.11a but add Type 4= -40 to +85C
Tx and Rx antenna port impedance=50ohms
11) What hooks are needed for frequency diversity/MIMO, etc... TJ, are you
including these in the future enhancements section?
12) Do you see most systems being 1 or 2 box solutions? If 2 boxes, should
add some recommended practice for standardization.
Let's get a dialog going and I'll try to provide a coordinated input to the
PHY spec.
Regards,
Drayt