Clusterhead Broadcast Channel (P-CHBCH,S-CHBCH) Signaling Format
[Framing and Channel Multiplexing]

This information is used to distribute physical resources during the TTI and some additional protocol information (association, QoS reservation, etc.). It is located in the first symbol in the TTI,$s_{\mathrm{CHBCH}}$. In the case of several clusterheads operating on the same carrier frequency, the CHBCH of adjacent clusters (i.e. those within range of the CHSCH) cannot collide and thus must be allocated different symbols in the TTI or use disjoint frequency carrier sets. The same is true of the CHBCH and MCH/RACH of adjacent clusters. The time/frequency allocation of CHSCH/MCH/RACH across several clusters must be accomplished in a distributed fashion based on the activation times of the different clusterheads and mobility of the clusters. This is beyond the scope of this preliminary specification.

The CHBCH must use the lowest spectral efficiency (highest sensitivity) coded-modulation format in order to be detectable at large distances. It will thus employ a rate 1/2 forward-error-correcting code with QPSK modulation Coded Modulation and H-ARQ. Information will be coded across $N_{\mathrm{s,CHBCH}}-1$ OFDM symbols using all non-zero carriers. Interleaving shall be performed across frequencies with depth $IntDepth_{\mathrm{CHBCH}}$. $IntDepth_{\mathrm{CHBCH}}$ shall be an integer divisor of $N_{\mathrm{d}}-N_{\mathrm{z}}$. Prior to forward-error correction coding, a CRC of length 32 bits shall be applied to the PDU arriving from the MAC layer interface.

Channel estimation can be obtained from the CHSCH which is located in the adjacent OFDM symbols. The CHSCH symbols shall be found starting in symbol number $\lfloor.5N_{\mathrm{symb}}\rfloor$ of the CHBCH.

The number of bits per TTI delivered by the MAC layer interface (FEC + CRC) bits is determined by the formula $(N_{\mathrm{symb}}-1)*(N_{\mathrm{d}}-N_{\mathrm{f}}) - 32$.

If $N_\mathrm{pilot}$ additional pilot symbols per OFDM symbol are required to handle large frequency offsets due to high-mobility (Doppler) or significant carrier frequency offsets due to the RF equipment, then these are to be placed at equally spaced positions starting from the first non-zero carrier in each CHBCH symbol. These simply puncture the coded bit sequence. Care must be taken when choosing the value of $N_\mathrm{f}$ with respect to $IntDepth_{\mathrm{CHBCH}}$ so that consecutive bits of the encoded sequence are not punctured. A judicious choice would take $IntDepth_{\mathrm{CHBCH}}$ and $N_{\mathrm{d}}-N_{\mathrm{z}}$ to be relatively prime.

In order to allow for multi-cell deployment the CHBCH can use a reduced set of subbands which is controlled by the parameter $FreqReuse$. It should be set to the maximum number of base stations. Let $N_{FreqGroup}$ be the number of carriers of one frequency group. Then, the set of carriers used by the $i^\mathrm{th}$ CHBCH $i=1,2,3$ (CHBCH 0 is unused) is given by $\left\{((i-1) FreqReuse N_{pilot} ) + k*N_{FreqGroup}, k=0,\cdots,N_{Pilots}-1\right\}$.

The transmit power of the CHBCH shall be adjustable by higher layers in order to control the detection range of the clusterhead. This value will be transfered via higher layer signaling so that nodes may perform open-loop power control. The following table summarizes the parameters of the CHBCH which are transfered from higher layers using the primitive PHY_CHBCH.

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