creating of id and refid

Dear all,

My xml is like below:

<simple-para>This paper provides two rule bases to control
administration of cisatracurium, a non-depolarizing neuromuscular
blocking agent. One rule base is extracted from the objective approach
of fuzzy modeling algorithm (FMA), and the other is from the
subjective approach of experts&#x2019; clinical experience. First, we
established the data-acquisition system to record the manual
neuromuscular block control during surgery. <grant-sponsor>After
collecting</grant-sponsor> <grant-number>15 patients</grant-number>
data control by cisatracurium, we extracted six rules from these data
via FMA. Another rule base also had six rules from experts
withclinical anesthesia experience.<simple-para>

I need to convert the <grant-sponser> to <grant-sponsor id="grs1">
I need to convert the <grant-number> to <grant-number refid="grs1">

My XSL is like below:

<xsl:template match="grant-sponsor">
		<grant-sponsor id="grs{position() - 1}">
			<xsl:apply-templates/>
		</grant-sponsor>
	</xsl:template>
	<xsl:template match="grant-number">
		<grant-number refid="{preceding-sibling::grant-sponsor/@id}">
			<xsl:apply-templates/>
		</grant-number>
	</xsl:template>

I am getting the empty refid. Please suggest how to solve this problem.

Regards,
Ganesh