[SOLVED] Inquiry: LTE blockers (Blocking Requirements for an LTE RX)

[MFayek]

Dear friends ,

While putting down the specs for an LTE receiver,I found a problem in the blocking requirements.
In the 3gpp stadnadrd , I found a table named narrow band blocker.but i cannot find the upper limit for the power of the blocker that the receiver should sustain .all text book that i've read say "take the blocker for 55dB "!!.
I really can't Understand this issue. Shouldn't the blocker signal have an upper limit for its power??!! but I can't find this limit.
I think that the blocker should be have a margin for each channel BW but what is shown the table that power is constant for all channel BW.

Could anyone clarify this issue ?? any help appreciated
the table from the standard :

 

[Mazz]

The upper limit is always -55 dBm, for each case.

The spec states that you have to apply a useful signal that is higher than the reference sensitivity by 22 dB (for example in the 1.4MHz channel BW) and verify that with an interferer at -55 dBm the throughput shall be ≥ 95% of the maximum throughput of the reference measurement channels as specified in Annexes A.2.2, A.2.3 and A.3.2.

The interferer power is always the same but the useful signal to consider depends on channel BW.

I think there is no issue in this statement.

I hope it can help.

Mazz

 

[vfone]

-55dBm is a system spec requirement used to pass an FTA (Full Type Approval).
If you are an RFIC chip designer always to the -55dBm level you should add a good margin (at least 3dB).

 

[MFayek]

Thanks for your replies,

The spec states that you have to apply a useful signal that is higher than the reference sensitivity by 22 dB (for example in the 1.4MHz channel BW) and verify that with an interferer at -55 dB
Mazz

I'm confused about applying a useful signal ,how can i apply a useful signal to the received signal?? isn't that related to the specs of a transmitter PA?
I think that i misunderstood what u typed.Could you make a bit clearer

---------- Post added at 16:02 ---------- Previous post was at 15:55 ----------

-55dBm is a system spec requirement used to pass an FTA (Full Type Approval).
If you are an RFIC chip designer always to the -55dBm level you should add a good margin (at least 3dB).

Is it just for passing the FTA,How can i take it into consideration in my design of the Rx ?
I understand this as a spec for the filters in my RX .Am i right??

 

[Mazz]

MFayek

you are testing a receiver. What I mean with useful signal is the wanted inband signal that satisfy the receiver requirements (sensitivity).

The procedure tells you to increase this signal by a certain amount respect to the sensitivity level (22 dB in the example) and add an interferer at -55dBm.

Verify if the received signal still meets the requirements and you're done.

Mazz

 

[MFayek]

Really Appreyiate your help ,

you are testing a receiver.

Mazz

This is the main point that confuse me in the standard and many textbooks .
Now I'm designing a Receiver ,Why am i talking about testing??
Isn't testing is a final step in designing a system to be sure that it meets the specs that i've put in the first phase in the design.
The question here,how to put this data for blockers in my specs to take into consideration while going further in the design of each block in the Rx?

Thanks for your help,

 

[Mazz]

Let me suggest you a good reading in RF system design: Qizheng Gu, RF system design of transceivers for wireless communications

Here you'll find all the informations you need to pass from system specs to block specs. It is not something we can discuss in detail in a post, it is the whole job of some designer!

Mazz

 

[MFayek]

Dear Mazz ,
Thanks for you suggestion of this book. I've spent the last month reading it beside my final exams
Thanks for your help

Mohsen

 

[RFDave]

If you think about the blocker, it's at a much higher level then the desired signal on channel. You need to make sure that your receiver has enough filtering so that when you reach the ADC, the blocker is at a low enough level that you have sufficient dynamic range for both the desired signal and the (Filter attenuated) blocker. A Second order effect is that the Phase Noise of the LO at the Blocker offset will also cause an interfering signal, so you have to budget for this.

 

[MFayek]

Dear RFDave,
thanks for ur reply. Actually the problem for me was the amount of attenuation needed by filters.As i've known, attenuating the blocker signal to be equal to the noise floor of the receiver will be enough ,is that ok? I think the same thing for adjacent channel selectivity.